Vehicle power supply system

ABSTRACT

A main power source is, for example, an ordinary Pb battery. At the time of starting an engine, the main power source supplies power to a starter. The main power source is given a higher priority than an auxiliary power source to supply power to ordinary loads. The auxiliary power source is a high performance battery (e.g., Li ion battery), which has superior charge acceptance capability and better state detectability over the main power source. The auxiliary power source stores regenerative power, which is generated by a generator at the time of deceleration of a vehicle, and is used as a redundant power source for the main power source. The main power source and the auxiliary power source are connected to each other through a supply circuit, which has a DC/DC converter, and a second supply circuit, which has a switch.

BACKGROUND

The invention relates to a vehicle power supply system having twobatteries (a main power source and an auxiliary power source).

A previously proposed vehicle power supply system having two batteries(2-battery system) is disclosed in, for example, JP-A-6-296332,JP-A-2001-186687 or U.S. Pat. No. 6,275,001.

The system set forth in JP-A-6-296332 includes a main power storagemeans and a backup power storage means, which are connected to eachother through a DC/DC converter. Switching of the DC/DC converter iscontrolled in such a manner that regenerative energy (electric power),which is obtained during deceleration of the vehicle, is stored in thebackup power storage means, and the stored electric power is suppliedfrom the backup power storage means to the electrical loads of thevehicle at time (e.g., time of accelerating the vehicle, time of steadydriving of the vehicle or time of idling the engine) other than the timeof decelerating the vehicle at a higher priority over the main powerstorage means.

The system set forth in JP-A-2001-186687 has a power supply networkbattery and a starter battery. The power supply network battery isconnected to a generator, and the starter battery is connected to astarter. These batteries are connected to each other through a DC/DCconverter and a switch. Here, the switch is provided in parallel withthe DC/DC converter.

The system set forth in U.S. Pat. No. 6,275,001 has a first battery, asecond battery and a generator. The first battery supplies electricpower to a starter at the time of starting the engine, and the secondbattery supplies electric power to electrical loads mounted on thevehicle. The generator charges the first battery and the second battery.With this construction, it is possible to supply power to the electricalloads from the second battery while power is supplied from the firstbattery to the starter to start the engine. Accordingly, there is nomomentary stop of electrical loads (e.g., a navigation system), whichwould be otherwise caused by a voltage drop of the first battery due toflow of a large current (surge current) in the initial stage ofsupplying electric power to the starter, and the voltage to theelectrical loads can be guaranteed by the second battery.

However, in the system set forth in JP-A-6-296332, there are thefollowing disadvantages. Firstly, regenerative energy generated by analternator during deceleration of the vehicle is stored in the backuppower storage means through the DC/DC converter. Thus, due to thepresence of the DC/DC converter between the alternator and the backuppower storage means, the recovery efficiency is decreased to causedeterioration of fuel consumption. Also, since power stored in thebackup power storage means also goes through the DC/DC converter at thetime of supplying electric power to the electrical loads of the vehicle,the power supply efficiency is decreased. Furthermore, the operatingvoltage of the DC/DC converter is applied from the main power storagemeans. Thus, if the main power storage means becomes inoperable (e.g.,at the time of battery death), energy recovery during decelerationbecomes impossible, and also electric power cannot be supplied from thebackup power storage means to the electrical loads. Thus, thereliability of the system is largely decreased.

In the system of JP-A-2001-186687, there are the followingdisadvantages. Firstly, since power generated by the generator issupplied to the starter battery through the DC/DC converter, energyefficiency is poor. Also, at the time of performing high powergeneration (e.g., regenerative power generation during vehicledeceleration) through use of the generator, large voltage fluctuationsact on the power supply network battery and the electrical loads. Thus,troubles, such as flickering of lights and wiper speed fluctuations,occur. A safety measure for counteracting with a failure of one of thepower supply network battery and the starter battery is not implementedfor important devices (e.g., safety devices, such as an electric brakingdevice, electric power steering device), which are among the electricalloads mounted on the vehicle and need stable electric power supply. Forexample, when the power supply network battery has shorted to the groundside, it is not possible to isolate the power supply network battery andto supply power to the important devices from the starter battery.

In the system set forth in U.S. Pat. No. 6,275,001, there are thefollowing disadvantages. That is, at the time of starting the engine,the respective roles of the first battery and the second battery arelimited, and engine starting is carried out with the first battery only.Thus, engine starting characteristics are not improved in comparison toan ordinary 1-battery vehicle power supply system.

For example, in a case of a vehicle equipped with an idle stop system(an eco-run system that automatically stops an engine at the time ofstopping the vehicle and then automatically controls restarting of theengine based on, for example, a signal indicative of releasing of abrake), it is desirable to restart the engine within a short period oftime at the time of moving the vehicle, for example, at the blue trafficsignal after the automatic stopping of the engine at, for example, theintersection. However, when power supply to the starter is carried outusing the first battery only, it is difficult to shorten the startingtime, and thus a significant advantage cannot be expected from thesystem set forth in U.S. Pat. No. 6,275,001 when the system isimplemented in the eco-run system.

The present invention addresses the above disadvantages, and it is afirst objective of the invention to provide a more reliable vehiclepower supply system, with which it is possible to efficiently recoverenergy regenerated during deceleration of a vehicle and also to supply astable voltage to electrical loads.

It is a second objective to provide a vehicle power supply system, withwhich it is possible to carry out recovery of energy regenerated duringdeceleration of a vehicle and supply of power to electrical loadsefficiently.

It is a third objective to provide a vehicle power supply system, withwhich it is possible to guarantee a voltage and furthermore shortenstarting time of an engine.

SUMMARY

To achieve the first objective mentioned above, a first aspect of thepresent application provides a vehicle power supply system including: agenerator, which is mounted on a vehicle; a main power source, to whichan ordinary load, such as a lamp or an audio device, is connected; anauxiliary power source, which is connected to the generator, wherein theauxiliary power source recovers regenerative electric power, which isgenerated by the generator using kinetic energy, such as kinetic energyof deceleration, or thermal energy, such as thermal energy of exhaustheat, and the auxiliary power source stores electric power that isgenerated by the generator; a first supply circuit, which connects theauxiliary power source to the main power source and the ordinary loadthrough a DC/DC converter; a second supply circuit, which is in parallelwith the first supply circuit and which connects the auxiliary powersource to the main power source and the ordinary load through a switch;and a control means for controlling operation of the DC/DC converter andoperation of the switch, wherein the control means is enabled to selectone of: a first control state, in which the DC/DC converter is driven,and the switch is opened; and a second control state, in which the DC/DCconverter is stopped, and the switch is closed.

With this construction, since regenerative energy can be recovereddirectly to the auxiliary power source from the generator withoutpassing through the DC/DC converter, energy recovery can be carried outefficiently. Since the main power source is charged by the auxiliarypower source via the first supply circuit and the second supply circuit(i.e. it is not connected to the generator directly), for example whenthe generator is carrying out regeneration during deceleration of thevehicle, no large voltage fluctuations act on the main power source, andit is possible to supply power stably to the electrical loads connectedto the main power source.

Since the control means can select a first control state and a secondcontrol state in correspondence with the running state of the vehicleand the charge states of the main power source and the auxiliary powersource, the efficiency of charging from the auxiliary power source tothe main power source or from the main power source to the auxiliarypower source can be raised.

The vehicle power supply system described above is preferablyconstructed so that the generator is driven by the engine, and theauxiliary power source, which is connected to the generator, recoversregenerative electric power, which is generated by the generator at timeof deceleration of a vehicle, and the auxiliary power source storeselectric power that is generated by the generator through driving of thegenerator by the engine.

With this construction, since energy regenerated during vehicledeceleration can be recovered directly to the auxiliary power sourcewithout going through the DC/DC converter, energy recovery can becarried out with good efficiency.

In the vehicle power supply system described above, the control meansmay be also enabled to select a third control state, in which the DC/DCconverter is driven, and the switch is closed. In this case, for examplewhen there is no surplus in the output capability of the DC/DCconverter, since power can be supplied from the auxiliary power sourceto the main power source or from the main power source to the auxiliarypower source with the third control state selected, the thermal affectscan be reduced.

In the vehicle power supply system described above, preferably the mainpower source has a greater nominal voltage or nominal capacity over theauxiliary power source. In this case, power can be supplied from themain power source to the auxiliary power source just by the switch beingturned on. Furthermore, since the voltage of the auxiliary power sourceis lower, the voltage difference between the generator and the auxiliarypower source is greater than in an ordinary combination of a generatorand a main power source only, and power generated by the generator canbe stored more efficiently.

In the vehicle power supply system described above, the main powersource has a smaller nominal voltage or nominal capacity over theauxiliary power source. In this case, when power regenerated duringdeceleration is stored in the auxiliary power source, since the voltageof the auxiliary power source is higher than that of the main powersource, regenerative electric power can be supplied to the ordinaryloads from the auxiliary power source just by turning on the switch.

In the vehicle power supply system described above, alternatively, thenominal voltage of the main power source may coincide with the nominalvoltage of the auxiliary power source. In this case, when powerregenerated during deceleration is stored in the auxiliary power source,the charge percentage of the auxiliary power source becomes higher thanthat of the main power source to cause an increase in the voltage of theauxiliary power source. Thus, regenerative power can be supplied fromthe auxiliary power source to the ordinary loads just by closing theswitch.

In the vehicle power supply system described above, preferably the mainpower source and the auxiliary power source have a common operationalrange, in which a working voltage of the main power source generallycoincides with a working voltage of the auxiliary power source. In thiscase, when one of the power sources has failed, redundancy of a powersource can be ensured easily, and the safety of the vehicle as dependenton the power supply system improves. When the second control state isselected and power is exchanged between the main power source and theauxiliary power source, voltage fluctuation caused by voltage differencewhen the switch is turned on/off can be suppressed. Also, with acombination of two power sources (main power source and auxiliary powersource) having a small voltage difference so that their working voltageshave ranges where they are approximately the same, when a seriesregulator is used as the DC/DC converter, voltage adjustment with thatseries regulator becomes possible (since the voltage difference is smalland thermal losses are small), and the power supply system can beconstructed cheaply. The reason why it can be made inexpensive is thatcompared to a commonly known switching-type DC/DC converter, theprovision of a reactor or the like for power supply noise reduction isunnecessary, and the construction becomes simple.

In the vehicle power supply system described above, preferably the mainpower source has superior low-temperature discharge characteristics overthe auxiliary power source. By connecting the starter to a main powersource having good low-temperature discharge characteristics, it ispossible to improve the startability of the engine at low temperatures.

In the vehicle power supply system described above, preferably theauxiliary power source has superior charge acceptance capability andbetter state detectability over the main power source. In this case,energy recovery during vehicle deceleration can be carried outefficiently.

In the vehicle power supply system described above, preferably, the mainpower source is one of a lead battery, a Li ion battery and a Nihydrogen battery, and the auxiliary power source is one of a leadbattery, a Li ion battery, a Ni hydrogen battery and an electricaldouble-layer capacitor. When lead batteries are used for the main powersource and the auxiliary power source, it is possible to keep down theircost and achieve both energy recovery during deceleration and stablepower supply to the ordinary loads. When a Li ion battery or a Nihydrogen battery is used as the main power source, the life of the powersupply system as a whole can be increased. When a Li ion battery, a Nihydrogen battery or an electrical double-layer capacitor is used as theauxiliary power source, the regeneration capability during decelerationcan be increased and its charge acceptance capability is also excellent.

In the vehicle power supply system described above, preferably, at timeof supplying power from the auxiliary power source to the main powersource and the ordinary load, the control means selects the secondcontrol state when the voltage of the auxiliary power source has fallento or below an allowable rated voltage of the ordinary load. In thiscase, power can be supplied with an efficient switch (the second supplycircuit) without applying stress to the ordinary loads.

In the vehicle power supply system described above, when a level ofpower supplied from the auxiliary power source to the main power sourceand the ordinary load, or a level of power supplied from the main powersource to the auxiliary power source and the ordinary load, is called asa power supply level, the control means selects one of the first controlstate and the second control state in accordance with the power supplylevel. Since the characteristics of the DC/DC converter and the switchdiffer (may be suitable or unsuitable) depending on the power supplylevel, by selecting either the first control state or the second controlstate in accordance with the power supply level it is possible tooptimize the combination.

In the vehicle power supply system described above, preferably thecontrol means selects the first control state when the power supplylevel is equal to or below a predetermined value, and the control meansselects the second control state when the power supply level is abovethe predetermined value. In this case, by using the DC/DC converter onlywhen the power level is low (the power supply level is below thepredetermined value), the DC/DC converter, which is more expensive thana switch, can be made low-capacity and its cost thereby kept down. Bythe switch being used when the power level is high (when the powersupply level is above the predetermined value), the supply efficiencycan be increased.

In the vehicle power supply system described above, the control meansmay select one of the first control state and the second control statein accordance with a voltage difference between the main power sourceand the auxiliary power source. In this case, the states of the mainpower source and the auxiliary power source can be sensed by theirvoltages only, and an optimal control state can be selected inaccordance with the sensed voltage difference between the two powersources.

In the vehicle power supply system described above, preferably thecontrol means selects the second control state when the voltagedifference between the main power source and the auxiliary power sourceis equal to or below a predetermined value, and the control meansselects the first control state when the voltage difference between themain power source and the auxiliary power source is above thepredetermined value. In this case, when the voltage difference betweenthe two power sources is large, the voltages can be adjusted in theDC/DC converter and supplied in a low voltage difference state, and whenthe voltage difference between the two power sources is small, the powercan be supplied with an efficient switch (the second supply circuit).

In the vehicle power supply system described above, when a level ofpower supplied from the auxiliary power source to the main power sourceand the ordinary load, or a level of power supplied from the main powersource to the auxiliary power source and the ordinary load, is called asa power supply level, the control means may select one of the firstcontrol state and the second control state in accordance with thevoltage difference between the main power source and the auxiliary powersource and the power supply level. By selecting the control state basedon both the power supply level and the voltage difference between thetwo power sources instead of the power supply level alone or the voltagedifference between the two power sources alone, it is possible to selecta more optimal control state.

In the vehicle power supply system described above, preferably, thecontrol means first selects the first control state when the voltage ofthe auxiliary power source is higher than that of the main power sourceand also the power level supplied from the auxiliary power source to themain power source and the ordinary load is greater than a predeterminedvalue and the control means then shifts from the first control state tothe second control state after the voltage of the auxiliary power sourcefalls to or below the allowable rated voltage of the ordinary load. Inthis case, no overvoltage is applied to electrical loads such as lights,and reduction in the lives of the electrical loads can be suppressed.Efficient power supply using a switch becomes possible.

In the vehicle power supply system described above, preferably, thereare further provided third and fourth supply circuits. The third supplycircuit supplies electric power from the auxiliary power source to animportant load, which is involved in a basic running operation or asafety operation of the vehicle. The fourth supply circuit supplieselectric power from the main power source to the important load, whereineach of the third supply circuit and the fourth supply circuit has adiode, which limits a reverse flow of an electric current therethrough.With this construction, since it is possible to provide redundancy of apower source with respect to the important loads, even when one or theother of the main power source and the auxiliary power source hasfailed, power can be supplied to the important loads without fail, andthe safety of the vehicle improves. By the third supply circuit and thefourth supply circuit each being provided with a diode, since reversecurrents can be prevented with certainty, a stable power supply to theimportant loads can be ensured.

In the vehicle power supply system described above, preferably, thereare further provided third and fourth supply circuits, which aredifferent from the above ones. The third supply circuit supplieselectric power from the auxiliary power source to an important load,which is involved in a basic running operation or a safety operation ofthe vehicle. The fourth supply circuit supplies electric power from themain power source to the important load, wherein the third supplycircuit has a diode, which limits a reverse flow of an electric currenttherethrough, in a case where the main power source has a higher nominalvoltage or nominal capacity over the auxiliary power source. With thisconstruction, since it is possible to provide redundancy of a powersource with respect to the important loads, even when one or the otherof the main power source and the auxiliary power source has failed,power can be supplied to the important loads without fail, and thesafety of the vehicle improves. By the third supply circuit beingprovided with a diode, since current can be prevented from flowingreversely through the third supply circuit from the main power source,which has a higher nominal voltage than the auxiliary power source, astable power supply to the important loads can be ensured. Also, since adiode is provided in the third supply circuit only, compared to a casewhere diodes are provided in both the third supply circuit and thefourth supply circuit, a reduction in cost corresponding to thereduction in the number of diodes is possible. Furthermore, when poweris supplied to the important loads from the main power source, the powercan be supplied efficiently, without suffering a loss due to a diode.

In the vehicle power supply system described above, preferably, thereare further provide third and fourth supply circuits, which aredifferent from the above ones. The third supply circuit supplieselectric power from the auxiliary power source to an important load,which is involved in a basic running operation or a safety operation ofthe vehicle, and the fourth supply circuit supplies electric power fromthe main power source to the important load, wherein the fourth supplycircuit has a diode, which limits a reverse flow of an electric currenttherethrough, in a case the main power source has a lower nominalvoltage or nominal capacity over the auxiliary power source. With thisconstruction, since it is possible to provide redundancy of a powersource with respect to the important loads, even when one or the otherof the main power source and the auxiliary power source has failed,power can be supplied to the important loads without fail, and thesafety of the vehicle improves. By the fourth supply circuit beingprovided with a diode, since current can be prevented from flowingreversely through the fourth supply circuit from the auxiliary powersource, which has a higher nominal voltage than the main power source, astable power supply to the important loads can be ensured. Also, since adiode is provided in the fourth supply circuit only, compared to a casewhere diodes are provided in both the third supply circuit and thefourth supply circuit, a reduction in cost corresponding to thereduction in the number of diodes is possible. Furthermore, when poweris supplied to the important loads from the auxiliary power source, thepower can be supplied efficiently, without suffering a loss due to adiode.

In the vehicle power supply system described above, preferably, thecontrol means opens the switch when one of the main power source and theauxiliary power source fails in a state where the second control stateis selected by the control means. For example, when the main powersource has failed (e.g., grounded), since by turning the switch off itis possible to separate the failed main power source from the auxiliarypower source, power can be supplied stably from the auxiliary powersource to the important loads, and the redundancy of a power source withrespect to the important loads can be ensured.

In the vehicle power supply system described above, preferably, thecontrol means opens the switch when short-circuiting occurs between acathode and an anode of one of the main power source and the auxiliarypower source. Since this separates the main power source from theauxiliary power source, redundancy of a power supply to the ordinaryloads from the power source functioning normally can be realized.

In the vehicle power supply system described above, preferably, thecontrol means opens the switch when performance of the main power sourcefalls. Since this separates the main power source from the auxiliarypower source, redundancy of a power supply to the ordinary loads fromthe auxiliary power source can be realized.

In the vehicle power supply system described above, preferably, thecontrol means opens the switch when performance of the auxiliary powersource falls. Since this separates the main power source from theauxiliary power source, redundancy of a power supply to the ordinaryloads from the main power source can be realized.

In the vehicle power supply system described above, preferably, thecontrol means stops the DC/DC converter when one of the main powersource and the auxiliary power source fails in a state where the firstcontrol state is selected by the control means. For example when themain power source has failed (e.g., grounded), since by stopping theDC/DC converter it is possible to separate the failed main power sourcefrom the auxiliary power source, power can be supplied stably from theauxiliary power source to the important loads, and redundancy of a powersource with respect to the important loads can be ensured.

In the vehicle power supply system described above, preferably, thecontrol means switches from the second control state to the thirdcontrol state when a temperature of the switch is increased beyond apredetermined value in a state where the second control state isselected by the control means. In this case, when the temperature of theswitch rises above the predetermined value, since the second supplycircuit having the switch and the first supply circuit having the DC/DCconverter are used together to supply power, heating of the switch canbe suppressed.

In the vehicle power supply system described above, the ordinary load,which is connected to the main power source, may include an electricalload, which requires a dark current after stopping of the engine. Thedark current is a current that is required to maintain a minimumfunction of the electrical load even when an ignition key of the vehicleis turned off. In this case, after the engine has stopped, with respectto the electrical loads needing a dark current from the main powersource, power can be supplied from the main power source.

In the vehicle power supply system described above, preferably, at timeof shifting from the first control state to the second control state orat time of shifting from the second control state to the first controlstate, the control means increases an output voltage of the DC/DCconverter to a higher one of a voltage of the main power source and avoltage of the auxiliary power source or decreases the output voltage ofthe DC/DC converter to a lower one of the voltage of the main powersource and the voltage of the auxiliary power source, and then thecontrol means shifts from the first control state to the second controlstate or shifts from the second control state to the first controlstate. Since this makes it possible to suppress voltage fluctuationsoccurring when the control state is changed over, flickering of lightsand so on can be prevented.

In the vehicle power supply system described above, preferably, thecontrol means senses a working sate, such as a temperature or a voltage,of the DC/DC converter in a state where the first control state isselected by the control means, and the control means shifts from thefirst control sate to the second control state when the sensed workingstate of the DC/DC converter exceeds a predefined value. In this case,since it is possible to keep the working state of the DC/DC converterwithin a predefined value, failure of the DC/DC converter can beprevented and the DC/DC converter can be made small.

In the vehicle power supply system described above, preferably, thecontrol means makes an output voltage of the DC/DC converter generallyequal to an output voltage of the generator. In this way, it is possibleto limit voltage fluctuations of the main power source, and thereby itis possible to implement stable voltage supply to the electrical loads.Furthermore, a contact arcing of the switch provided in the second powersupply circuit can be made small to allow a size reduction.

In the vehicle power supply system described above, preferably, thecontrol means may control an output voltage of the generator such thatthe output voltage of the generator generally coincides with an outputvoltage of the DC/DC converter when the first control state is selectedby the control means. Since this makes it possible to suppress voltagefluctuation of the main power source, it is possible to realize a stablevoltage supply to the electrical loads. Contact arcing of the switchprovided in the second supply circuit can be made small and the switchcan be made small.

In the vehicle power supply system described above, the control meansmay sense a charge acceptance capability of the main power source basedon an output state of the DC/DC converter when the first control stateis selected by the control means. In this case, since it is notnecessary for the charge acceptance capability of the main power sourceto be sensed with a sensor, a low-cost system can be realized.

In the vehicle power supply system described above, the control meansmay sense a voltage of the auxiliary power source and an output voltageof the DC/DC converter based on a running state of the vehicle, and thecontrol means may control an output of the generator based on a sensedresult of the voltage of the auxiliary power source and of the outputvoltage of the DC/DC converter. By this means it is possible to controlthe output of the generator efficiently in accordance with the runningstate of the vehicle.

In the vehicle power supply system described above, the auxiliary powersource may supply electric power to an electrical load, which does notrequire a dark current. For example, with respect to battery death ofthe main power source that would normally occur when the vehicle isparked for a long period or left with a door half-open, by cutting thepower supply to devices of which resetting is allowable, it is possibleto prevent life and performance reduction of the main power source, andwith respect to electrical loads not needing a dark current, power canbe supplied from the auxiliary power source.

The electrical load, which does not require the dark current, may be oneof an electrical load, such as an ECU that does not have an internalmemory, and an electrical load, such as an ECU that always uses aninitial constant of an internal memory.

In the vehicle power supply system described above, there may be furtherprovided a dark current blocking means for blocking the dark current,wherein the auxiliary power source supplies electric power to anelectrical load (e.g., an electrical load, such as an ECU, which allowsresetting of its internal memory), which enables blocking of darkcurrent. By this means, even when dark current has been blocked by thedark current blocking means, power can be supplied from the auxiliarypower source.

In the vehicle power supply system described above, an auxiliary powersource switch may be connected in series with the auxiliary powersource. In this case, for example when the auxiliary power source hasfailed, since the auxiliary power source can be separated from the mainsystem by the auxiliary power source switch being turned off, the safetyof the main system can be ensured.

In the vehicle power supply system described above, preferably, theauxiliary power source switch is disposed between the generator and theauxiliary power source in such a manner that the auxiliary power sourceswitch is positioned on a generator side of an input side connection ofthe DC/DC converter. In this case, the input voltage of the DC/DCconverter can be limited to the voltage of the auxiliary power source,and the cost of the DC/DC converter can be reduced.

In the vehicle power supply system described above, the DC/DC convertermay include a series regulator. The objective of this is to remove noisecaused by power device switching by taking advantage of the fact thatthe voltage difference between the main power source and the auxiliarypower source is small (or their voltages are the same), and by thismeans it is possible to prevent the circuit being complicated by noisecountermeasures.

In the vehicle power supply system described above, preferably, in acase where a fully charged state of the auxiliary power source is sensedat time of performing regenerative power generation of the generatorduring, for example, deceleration of the vehicle, the generator carriesout the regenerative power generation at a voltage that is lower than avoltage of the auxiliary power source measured in the fully chargedstate of the auxiliary power source and supplies electric power to theordinary load in one of the first control state and the second controlstate. When the auxiliary power source is charged further after it hasbecome fully charged, there is a risk of battery deterioration or thelike caused by overcharging. To avoid this, preferably, when it has beensensed by voltage or charge level detecting means or the like that theauxiliary power source is fully charged, the generator is controlled toa voltage such that it cannot charge the auxiliary power source (a lowervoltage than the that of the auxiliary power source), and power supplyto the ordinary loads is effected by means of the first control state orthe second control state. In this case, for example on roads such aslong downhill slopes, even after the auxiliary power source has becomefully charged by regenerative power generation, by consumingregenerative electric power with the ordinary loads, it is possible toutilize the regenerative electric power effectively.

In the vehicle power supply system described above, in a case where afully charged state of the auxiliary power source is sensed at time ofperforming regenerative power generation of the generator during, forexample, deceleration of the vehicle, the generator may carry out theregenerative power generation at a voltage that is lower than a voltageof the auxiliary power source measured in the fully charged state of theauxiliary power source and may supply electric power to the ordinaryload in one of the first control state, the second control state and thethird control state.

In the vehicle power supply system described above, the main powersource may be maintained in a fully charged state in the first controlstate. By the battery state of the main power source being sensed basedon a battery voltage or discharge current and power from the auxiliarypower source or the generator being supplied to the ordinary loads usingthe DC/DC converter (the first control state), it is possible to keepthe main power source in a fully charged state. By this means, whereaswhen the main power source is for example a lead battery or the like aphenomenon of the battery life deteriorating due to cumulative dischargeis known, this can be suppressed and increased life can be achieved.

Next, to achieve the second objective mentioned earlier, a second aspectof the present application provides a vehicle power supply systemincluding: a generating means for generating regenerative energy at timeof decelerating a vehicle; a high-performance main power storage meansfor directly storing the regenerative energy, which is generated by thegenerating means, and for supplying electric power to an electricalload, which is mounted on the vehicle; an auxiliary power storage meansfor receiving and storing the electric power supplied from the mainpower storage means, wherein the auxiliary power storage means hassuperior discharge characteristics at a low temperature over the mainpower storage means; and a starting device power source switching meansfor selecting one or both of the main power storage means and theauxiliary power storage means as a power source based on an enginestarting temperature to supply electric power to a starting device forstarting an engine at time of starting the engine, wherein an enginetemperature or an engine temperature related temperature, which ismeasured at the time of starting the engine, is called as the enginestarting temperature.

With the construction described above, since regenerative energyproduced by the generating means during deceleration of the vehicle isdirectly recovered to the high-performance main power storage meanswithout passing through a DC/DC converter or the like, the recoveryefficiency can be increased. Furthermore, since power is supplied to theelectrical loads from this main power storage means without passingthrough a DC/DC converter or the like, power supply can be effectedefficiently. Also, since one or the other of the main power storagemeans and the auxiliary power storage means is selected or both are usedtogether as the power supply of the starting device in correspondencewith the engine starting temperature, the main power storage means andthe auxiliary power storage means can be used effectively in accordancewith their respective characteristics.

In the vehicle power supply system according to this second aspect ofthe application, preferably, a temperature range below a predeterminedtemperature T1 is called as an extremely low temperature range; atemperature range between the predetermined temperature T1 and apredetermined temperature T2 (T1<T2) is called as a low temperaturerange; a temperature range between the predetermined temperature T2 anda predetermined temperature T3 (T2<T3) is called as a normal temperaturerange; a temperature range above the predetermined temperature T3 iscalled as a high temperature range; the starting device power sourceswitching means selects the main power storage means when the enginestarting temperature is in the normal temperature range; and thestarting device power source switching means switches to use both themain power storage means and the auxiliary power storage means when theengine starting temperature is in one of the extremely low temperaturerange and the high temperature range. With this construction, since itis possible to select the main power storage means, which is optimal foruse in the normal temperature range, or both of the storage meanstogether, which can supply a larger power, under the large torqueconditions of the extremely low temperature range and the hightemperature range, the two storage means (the main power storage meansand the auxiliary power storage means) can be used effectively. By thismeans it is possible to make the storage means small and low in cost.

In the vehicle power supply system according to the second aspect,preferably, the auxiliary power storage means may supply electric powerto the starting device at the time of starting the engine when theengine starting temperature is in the low temperature range. With thisconstruction, since it is possible to reduce the temperature range overwhich the main power storage means and the auxiliary power storage meansare used together, a stable supply of power using the storage means notbeing used for starting, which will be discussed below, is possible.

In the vehicle power supply system of the second aspect, preferably, theauxiliary power storage means supplies electric power to the electricalload, which requires a guaranteed voltage, when the main power storagemeans supplies electric power to the starting device at the time ofstarting the engine, and the main power storage means supplies electricpower to the electrical load, which requires the guaranteed voltage,when the auxiliary power storage means supplies electric power to thestarting device at the time of starting the engine. When a large currentflows to the starting device from the main power storage means or theauxiliary power storage means, the main power storage means or theauxiliary power storage means suffers a voltage drop. With respect tothis, when the engine starting temperature is in the normal temperaturerange, since power is supplied to the starting device from the mainpower storage means, by supplying power to the electrical loads thatneed a guaranteed voltage from the auxiliary power storage means, it ispossible to secure the required voltage to the electrical loads needinga guaranteed voltage without suffering an affect of the voltage drop ofthe main power storage means. When the engine starting temperature is inthe low temperature range (including the extremely low temperaturerange) or the high temperature range, since power is being supplied tothe starting device from the auxiliary power storage means, by supplyingpower to the electrical loads needing a guaranteed voltage from the mainpower storage means, it is possible to secure the required voltage tothe electrical loads needing a guaranteed voltage without suffering anaffect of the voltage drop of the auxiliary power storage means.

In the vehicle power supply system of the second aspect, preferably,there is provided an automatic engine stopping/starting control device,which automatically controls stopping and restarting of an engine, and astarting device power source switching means selects the auxiliary powerstorage means at time of starting the engine first time and selects themain power storage means at time of restarting the engine through use ofthe automatic engine stopping/starting control device. With thisconstruction, since either the main power storage means or the auxiliarypower storage means is selected as the power source of the startingdevice depending on whether the engine is being started for the firsttime or being restarted after being automatically stopped, the mainpower storage means and the auxiliary power storage means can be usedeffectively in accordance with their respective characteristics.

In the vehicle power supply system of the second aspect, preferably, themain power storage means provides electric power to the electrical load,which requires a guaranteed voltage, at the time of starting the enginefirst time, and the auxiliary power storage means provides electricpower to the electrical load, which requires the guaranteed voltage, atthe time of restarting the engine through use of the automatic enginestopping/starting control device. When a large current flows to thestarting device from the main power storage means or the auxiliary powerstorage means, the main power storage means or the auxiliary powerstorage means suffers a voltage drop. With respect to this, when theengine is being started for the first time, since power is supplied tothe starting device from the auxiliary power storage means, by supplyingpower to the electrical loads that need a guaranteed voltage from themain power storage means, it is possible to secure the required voltageto the electrical loads needing a guaranteed voltage without sufferingan affect of the voltage drop of the auxiliary power storage means. Whenthe engine is being restarted after being automatically stopped, sincepower is supplied to the starting device from the main power storagemeans, by supplying power to the electrical loads needing a guaranteedvoltage from the auxiliary power storage means it is possible to securethe required voltage to the electrical loads needing a guaranteedvoltage without suffering an affect of the voltage drop of the mainpower storage means.

In the vehicle power supply system of the second aspect, preferably, themain power storage means provides electric power to the electrical loadwhile the engine is automatically stopped. In a vehicle in whichstopping and restarting of the engine are automatically controlled,since the frequency of automatic engine stops is inevitably high, it isdesirable to prevent deterioration of the auxiliary power storage meansby supplying power to the electrical loads from the high-performancemain power storage means.

In the vehicle power supply system of the second aspect, preferably,there is further provided a state sensing means for sensing a chargestate of the main power storage means, wherein when it is determinedthat the main power storage means alone is not enough to supply start-upelectric power to the starting device based on a sensed result of thestate sensing means, the start-up electric power is supplied to thestarting device from the auxiliary power storage means alone or fromboth the auxiliary power storage means and the main power storage means.By this means it is possible to effect restarting of the engine after anautomatic stop without fail.

In the vehicle power supply system of the second aspect, there may befurther provided a charging circuit, which supplies electric power fromthe main power storage means to the auxiliary power storage means, andthe charging circuit includes a DC/DC converter, and the auxiliary powerstorage means is charged with a micro current, which is supplied fromthe main power storage means to the auxiliary power storage meansthrough the DC/DC converter. With this construction, since the auxiliarypower storage means is charged with a micro current from the main powerstorage means, the DC/DC converter can be made small (low-capacity).

In the vehicle power supply system of the second aspect, there may befurther provided a charging circuit, which supplies electric power fromthe main power storage means to the auxiliary power storage means,wherein the charging circuit includes a relay switch, and the auxiliarypower storage means is charged with electric power supplied from themain power storage means when the relay switch is turned on. With thisconstruction, since the auxiliary power storage means can be chargedfrom the main power storage means without the interposition of a DC/DCconverter, the charging efficiency can be made high.

In the vehicle power supply system of the second aspect, preferably,when a voltage difference between the main power storage means and theauxiliary power storage means is smaller than a predetermined value, theDC/DC converter is operated, or the relay switch is turned on, so thatthe auxiliary power storage means is charged with electric powersupplied from the main power storage means. In this case, since theauxiliary power storage means is charged from the main power storagemeans with a micro current, heat losses due to resistance of the DC/DCconverter, the relay switch, wiring, and the two storage means can bereduced, and more efficient charging becomes possible.

In the vehicle power supply system of the second aspect, preferably, theauxiliary power storage means is charged with electric power suppliedfrom the main power storage means when the generating means stops itspower generating operation. Since the accuracy of detection of thecharging state of the main power storage means is good, it becomespossible for the charging power to be sensed with good accuracy.

In the vehicle power supply system of the second aspect, there may befurther provided two current sensing means and a voltage sensing means.One of the two current sensing means is provided in a conductor portion,which supplies electric power from the main power storage means to thestarting device and the electrical load, and the other one of the twocurrent sensing means is provided in a conductor portion, which supplieselectric power from the main power storage means to the auxiliary powerstorage means. The voltage sensing means is for sensing a voltage of themain power storage means, wherein a measured value of each currentsensing means and a measured value of the voltage sensing means arecompared with a measured value of the charge state of the main powerstorage means obtained through the state sensing means, so that a powerconsumption level and a charge level of the auxiliary power storagemeans are sensed with relatively high accuracy. In this way, it becomespossible to make up the consumed power using a precise state detectionvalue of the main power storage means, and the management of electricalenergy becomes easy. Even if the detection precision of the charge stateof the auxiliary power storage means itself is poor (the detectionprecision of lead batteries, which is one example of the auxiliary powerstorage means, is poor), if the power consumption of the electricalloads can be established precisely, by obtaining the difference betweenthis and the discharge level of the main power storage means it becomespossible to establish the charge state of the auxiliary power storagemeans more exactly.

In the vehicle power supply system of the second aspect, preferably,when the charge state of the main power storage means deviates from apredetermined state, the main power storage means is switched to theauxiliary power storage means to supply electric power to the electricalload, which requires the guaranteed voltage. By this means, even whenthe charge state of the main power storage means is other than apredetermined state, the required voltage can be supplied to theelectrical loads needing a guaranteed voltage from the auxiliary powerstorage means.

In the vehicle power supply system of the second aspect, preferably,supply of a dark current is performed from the main power storage meansafter the engine is stopped through operation of a key by a driver.

Next, to achieve the third objective mentioned earlier, a third aspectof the present application provides a vehicle power supply systemincluding: a generator, which is driven by an engine to generateelectric power; a first battery, which is charged with electric powergenerated by the generator; a second battery, which has an outputvoltage lower than that of the first battery, wherein the second batterysupplies electric power to a starter at time of starting the engine; acharging circuit, which supplies electric power from one of thegenerator and the first battery to the second battery; and an assistcircuit, which provides power assistance from the first battery to thestarter in addition to power supply from the second battery to thestarter.

With this construction, when at the time of engine starting power issupplied to the starter from the second battery, power assistance to thestarter from the first battery through the assist circuit is possible.In this case, since the first battery produces a higher voltage than thesecond battery, the output of the starter increases, and engine startingcan be completed sooner. Furthermore, since the output voltages of thefirst battery and the second battery are different and the first batteryproduces a higher voltage than the second battery, it is possible torealize the charging circuit provided between the two batteries with asimple construction.

In the vehicle power supply system of the third aspect of theapplication, preferably, the power assistance from the first battery isexecuted at a predetermined timing after initiation of the power supplyfrom the second battery to the starter. In this case, since power issupplied to the starter from only the second battery, which has a loweroutput voltage, in the initial stage of engine starting, the load on thestarter can be reduced in comparison to a case where power assistancewith the first battery, which has the higher output voltage, is carriedout from the beginning. Furthermore, since in the initial stage ofengine starting (before power assistance with the first battery isexecuted), power can be supplied to the electrical loads from the firstbattery, there is no momentary cutting off of electrical loads due to avoltage drop of the second battery caused by a large current (surgecurrent) flowing in the initial stage of excitation of the starter, andthe voltage to the electrical loads can be guaranteed.

In the vehicle power supply system of the third aspect, preferably, thepredetermined timing, at which the power assistance from the firstbattery is executed, is determined based on elapsed time since the timeof starting the engine or based on transition of a voltage value of thesecond battery. With this construction, since the timing at which toexecute power assistance can be determined without it being necessaryspecially to use a current sensor or the like, the control logic can besimplified and cost can be reduced.

In the vehicle power supply system of the third aspect, preferably, aninternal resistance per unit capacity of the first battery is smallerthan that of the second battery. When the internal resistance per unitcapacity of the first battery is smaller than that of the secondbattery, voltage drop on discharging is suppressed. Thus, a highervoltage can be applied to the starter, and the assisting effect can beincreased.

In the vehicle power supply system of the third aspect, preferably, thepower assistance from the first battery is stopped when the voltage ofthe first battery is lower than a predetermined value. When the chargestate of the first battery is low, there is little merit (earlierstarting of the engine) in power assistance. Thus, when the voltage ofthe first battery is below a predetermined value, power assistance withthe first battery is stopped.

In the vehicle power supply system of the third aspect, preferably, thesecond battery has superior low-temperature discharge characteristicsover the first battery. By allocating the first half of the enginestarting period, in which a large current flows through the starter, toa second battery having superior low-temperature dischargecharacteristics, it is possible to ensure engine starting at lowtemperatures also.

In the vehicle power supply system of the third aspect, preferably, thecharging circuit includes an ON-OFF means for turning on and turning offsupply of the electric power to the second battery at a certain timeratio (i.e., a ratio between an ON time period and an OFF time period),and the assist circuit includes one of a relay and a semiconductorswitch. By this means it is possible to make the charging circuit asimple construction having the ON-OFF means. The construction of theassist circuit also can be made simple by the use of a relay or asemiconductor switch.

As the ON-OFF means provided in the charging circuit, an electronicswitching device (e.g., a MOSFET) using a semiconductor can be used. Or,as the ON-OFF means provided in the charging circuit, a DC/DC convertercan be used. When a DC/DC converter is used as the ON-OFF means, theDC/DC converter is preferably provided in the generator. In this case,since it is possible to construct a charging circuit connected to thesecond battery from the first battery via the generator, the circuitconstruction of the system can be simplified.

In the vehicle power supply system of the third aspect, preferably,there is further provided a distributor, which is connected to the firstbattery and the second battery to control an output voltage of the firstbattery and an output voltage of the second battery, wherein supply ofelectric power to an important load, which is involved in a basicrunning operation or a safety operation of a vehicle, is carried outthrough the distributor. With this construction, since power can besupplied to the important electrical loads from either of the firstbattery and the second battery through the distributor, a guaranteedvoltage to the important electrical loads can be obtained, and thereliability and redundancy of the system as a whole increase.

In the vehicle power supply system of the third aspect, preferably, thefirst battery stores regenerative energy, which is generated by thegenerator at time of decelerating a vehicle. In this case, by theregenerative energy of deceleration being stored in a battery having asmall internal resistance per unit capacity, the regenerative energy canbe taken in more efficiently.

In the vehicle power supply system of the third aspect, preferably, thesecond battery provides dark current to an electrical load after theengine is stopped through operation of a key by a driver. With thisconstruction, by the supplying of dark current being allocated to thesecond battery, the load on the first battery is reduced. Thus, thefirst battery can be made smaller. As a result, for example when anexpensive Li ion battery or the like is used as the first battery, it ispossible to keep down its cost.

A vehicle power supply system according to the third aspect can beapplied to a vehicle that has an automatic engine stopping/startingcontrol device, which automatically controls stopping and restarting ofthe engine. With the third aspect, since engine starting can be effectedmore quickly, a highly beneficial effect can be obtained when the engineis restarted for example after it has been automatically stopped at, forexample, an intersection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electrical circuit diagram of a vehicle power supply systemaccording to a first embodiment.

FIG. 2 is a flowchart showing a control procedure for engine startingaccording to the first embodiment.

FIG. 3 is a voltage waveform graph of a main power source on enginestarting in the first embodiment.

FIG. 4 is a control flowchart of a power supply system according to asecond embodiment.

FIG. 5 is a control flowchart of a power supply system according to athird embodiment.

FIG. 6 is a graph illustrating regenerative charging during decelerationin the third embodiment.

FIG. 7 is a control flowchart of a power supply system according to thethird embodiment.

FIG. 8 is a control flowchart of a power supply system according to afourth embodiment.

FIG. 9 is a control flowchart of a power supply system according to afifth embodiment.

FIG. 10 is a control flowchart of a power supply system according to asixth embodiment.

FIG. 11 is an electrical circuit diagram of a power supply systemaccording to a seventh embodiment.

FIG. 12 is an electrical circuit diagram of a power supply systemaccording to the seventh embodiment.

FIG. 13 is an electrical circuit diagram of a power supply systemaccording to the seventh embodiment.

FIG. 14 is an electrical circuit diagram of a power supply systemaccording to an eighth embodiment.

FIG. 15 is an electrical circuit diagram of a power supply systemaccording to a ninth embodiment.

FIG. 16 is an electrical circuit diagram of a power supply systemaccording to a tenth embodiment.

FIG. 17 is an electrical circuit diagram of a power supply systemaccording to an eleventh embodiment.

FIG. 18 is an electrical circuit diagram of a power supply systemaccording to a twelfth embodiment.

FIG. 19 is an overall view of an engine starting system according to athirteenth embodiment.

FIG. 20 is a circuit diagram of a power supply system according to thethirteenth embodiment.

FIG. 21 is a flowchart showing battery switching control on enginestarting according to the thirteenth embodiment.

FIG. 22 is a flowchart showing a method of charging a sub-batteryaccording to the thirteenth embodiment.

FIG. 23 is a circuit diagram of a power supply system according to afourteenth embodiment.

FIG. 24 is an overall view of a power supply system for a vehicleaccording to a fifteenth embodiment.

FIG. 25 is a flowchart showing a control procedure for engine startingaccording to the fifteenth embodiment.

FIG. 26 is a view showing voltage changes of a first battery and asecond battery having different internal resistances per unit capacity.

FIG. 27 is an overall view of a vehicle power supply system in asixteenth embodiment.

FIG. 28 is a flowchart showing a control procedure for engine startingin the sixteenth embodiment.

FIG. 29 is an overall view of a vehicle power supply system in aseventeenth embodiment.

FIG. 30 is an overall view of a vehicle power supply system according toan eighteenth embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Best modes for practicing the invention will be described in detailbased on the following embodiments.

First Embodiment

FIG. 1 is an electrical circuit diagram of a power supply system(hereinafter, referred to as a power supply system S) for an automotivevehicle according to a first embodiment. FIG. 2 is a flowchart showing acontrol procedure for starting an engine.

The power supply system S includes a generator 1 and two power sources(a main power source 2 and an auxiliary power source 3) and supplieselectric power to electrical loads (described below) mounted on thevehicle. The generator 1 is driven by the engine (not shown).

The generator 1 is an alternator, which has an IC regulator. Thegenerator 1 is driven by the engine through a drive belt and generates avoltage of, for example, 13 to 14 V. The generator 1 is connecteddirectly to the auxiliary power source (sub-power source) 3 and is alsoconnected to the main power source 2 through a power supply circuitdescribed below.

The power supply circuit includes a first supply circuit 5 and a secondsupply circuit 7, which are connected in parallel between the auxiliarypower source 3 and the main power source 2. The first supply circuit 5includes a DC/DC converter 4, which uses, for example, a seriesregulator. The second supply circuit 7 includes a switch 6. Although inFIG. 1, a relay-type switch 6 is shown in the second supply circuit 7, asemiconductor switch may be alternatively used instead of the relay-typeswitch 6.

The main power source 2 is, for example, an ordinary Pb (lead) batteryand produces a voltage of 12 to 13 V (nominal voltage 12 V). The mainpower source 2 is given a higher priority for supplying electric powerto the ordinary electrical loads 8 than the auxiliary power source 3.Important loads (further discussed later), which are involved in a basicrunning operation and a safety operation of the vehicle, are connectedto the main power source 2 through a third supply circuit 9. The thirdsupply circuit 9 includes diodes 10, 11, which limit a reverse flow ofan electric current from the auxiliary power source 3 side.

The auxiliary power source 3 is a high-performance battery (e.g., aLithium ion battery), which has superior charge acceptance capabilityover the main power source 2 and which allows easy state detection.Furthermore, the auxiliary power source 3 has a smaller internalresistance per unit capacity over the main power source 2 and produces avoltage of, for example, 9 to 12 V (nominal voltage 10.8 V). Theauxiliary power source 3, for example, recovers regenerative electricpower, which is generated by the generator 1 during deceleration of thevehicle. Also, the auxiliary power source 3 stores other electric powergenerated by the generator 1 such as electric power generated by thegenerator 1 in a non-deceleration period. The above-mentioned importantloads are connected to the generator 1 and the auxiliary power source 3through a fourth supply circuit 12. The fourth supply circuit 12includes a diode 13, which limits a reverse flow of an electric currentfrom the main power source 2 side.

The above-mentioned ordinary loads 8 include a starter 8 a and otherordinary loads 8 b mounted on the vehicle. The starter 8 a starts(cranks) the engine. The other ordinary loads 8 b include, for example,lamps, wipers, audio devices and an air-conditioning system. Again, themain power source 2 is given the higher priority for supplying electricpower to these ordinary loads 8 b than the auxiliary power source 3.However, when a power supply capability of the main power source 2 isreduced to a low level, the auxiliary power source 3 or the generator 1is used to supply electric power to the ordinary loads 8 b.

The important loads, which are involved in the basic running operationand the safety operation of the vehicle, include, for example, a controlunit (hereinafter, referred to as a safety ECU 16) and an electroniccontrol unit (hereinafter, referred to as a system ECU 17). The controlunit (the safety ECU 16) electronically controls various actuators 14through a relay 15. The actuators 14 are involved in the basic runningoperation and/or the safety operation of the vehicle. The electroniccontrol unit (the system ECU 17) electronically controls the powersupply system S (e.g., the generator 1, the DC/DC converter 4, theswitch 6). Even in a case where either the main power source 2 or theauxiliary power source 3 fails, the important loads can directly receiveelectric power from the remaining one of the main power source 2 and theauxiliary power source 3. That is, redundancy of a power source withrespect to the important loads is provided.

The system ECU 17 can appropriately select one of a first control state,a second control state and a third control state, which are discussedbelow, depending on the operational state of the DC/DC converter 4 andthe switch 6.

The first control state is for supplying electric power through use ofthe first supply circuit 5. In the first control state, the DC/DCconverter 4 is driven (ON), and the switch 6 is opened (OFF). The secondcontrol state is for supplying electric power through use of the secondsupply circuit 7. In the second control state, the DC/DC converter 4 isstopped (OFF), and the switch 6 is closed (ON). The third control stateis for supplying electric power through use of both the first supplycircuit 5 and the second supply circuit 7. In the third control state,the DC/DC converter 4 is driven (ON), and the switch 6 is closed (ON).

Next, a control procedure of the system ECU 17 at the time of startingthe engine will be described with reference to a flowchart shown in FIG.2.

At step 10, an IG key (ignition key), which is an engine start switch,is turned to an ST position (a position for supplying electric power tothe starter 8 a). At step 11, power is supplied from the main powersource 2 to the starter 8 a. At step 12, it is determined whether theoutput voltage of the auxiliary power source 3 is equal to or above afixed value. The voltage of the auxiliary power source 3 can be sensedby, for example, a voltmeter 18 shown in FIG. 1. When the result of thisdetermination is YES, control proceeds to the following step 13. Incontrast, when the determination result is NO, control jumps to step 15where the supply of electric power from the auxiliary power source 3 tothe starter 8 a is stopped.

At step 13, a timing for supplying electric power from the auxiliarypower source 3 to the starter 8 a is determined. Specifically, it isdetermined whether the voltage across the terminals of the main powersource 2 has recovered to a predetermined voltage. Alternatively, it maybe determined whether fixed time has elapsed from the start of powersupply to the starter 8 a. As shown in FIG. 3, the voltage across theterminals of the main power source 2 drops sharply when a large currentflows to the starter 8 a in an initial stage and then gradually recoverswhile dipping slightly each time a piston passes a top dead center.Accordingly, it is possible to determine the timing for supplyingelectric power from the auxiliary power source 3 to the starter 8 a bymonitoring the voltage across the terminals of the main power source 2.

At step 14, when the determination result of step 13 is YES, the switch6 provided in the second supply circuit 7 is switched on, i.e., turnedon, so that power is supplied from the auxiliary power source 3 to thestarter 8 a through the second supply circuit 7 (this will be calledpower assistance). At step 15, it is determined whether the engine hasstarted. This starting determination can be made based on, for example,the engine speed or the voltage across the terminals of the main powersource 2. When the result of this determination is NO, control proceedsto step 16. In contrast, when the determination result is YES, controlproceeds to step 17. At step 16, the engine start operation is carriedout once again. At step 17, the IG key is turned from the ST position toan OFF position, and the present control operation is terminated.

According to the first embodiment, by performing the power assistancethrough use of the auxiliary power source 3 at the predetermined timingafter the initiation of the power supply from the main power source 2 tothe starter 8 a, the output of the starter 8 a is increased, and theengine can be started more quickly. In particular, in a vehicle equippedwith an automatic stopping and restarting device (idle stop device),each time the engine is restarted after being automatically stopped, thestarting feeling experienced by the occupants of the vehicle can beimproved since the starting time is shorter.

Furthermore, there are the two electric power supply paths to the safetyECU 16, which is an important load. These two power supply paths includea first supply path, which connects the main power source 2 to thesafety ECU 16 through the third supply circuit 9, and a second supplypath, which connects the auxiliary power source 3 to the safety ECU 16through the fourth supply circuit 12. Thus, even when one of the twopower sources or one of the two paths fails, power can be still suppliedby means of the remaining power source and the remaining path, therebyimplementing the redundancy. Furthermore, since the third supply circuit9 and the fourth supply circuit 12 are provided with the diodes 10 and13, respectively, for limiting a reverse flow of current, the two powersources (the main power source 2 and the auxiliary power source 3) arenever connected to each other through the third supply circuit 9 or thefourth supply circuit 12.

In the first embodiment, as the exemplary case of regenerative powergeneration, there is described the case where electric power isgenerated using the kinetic energy available during the deceleration ofthe vehicle. Besides this, the present invention can be equally appliedto, for example, the power generation using thermal energy of exhaustheat or cooling heat of the engine, or to the power generation usingflow energy of exhaust gas. Such power generations also include those inwhich electric power is generated directly from thermal energy using athermoelectric device and those in which thermal energy is firstconverted into kinetic energy, and then electric power is generated fromit.

Also, in the case of the power supply system S set forth in the firstembodiment, the main power source 2 has the higher output voltage(nominal voltage) over the auxiliary power source 3. However, it shouldbe noted that the present invention is equally applicable to a casewhere the auxiliary power source 3 has a higher output voltage (nominalvoltage) than the main power source 2. For example, the main powersource 2 may produce a voltage of 12 to 13 V (nominal voltage 12 V) asin the first embodiment, and the auxiliary power source 3 may produce avoltage of 12 to 16.4 V (nominal voltage 14.4 V). In such an instance,since the output voltage of the auxiliary power source 3 is higher, thegenerating capacity of the generator 1 should be correspondingly high toproduce a voltage of 13 to 17 V.

Further alternatively, the output voltage (nominal voltage) of the mainpower source 2 may be set to be the same as the output voltage (nominalvoltage) of the auxiliary power source 3. In this case, whenregenerative electric power derived from the deceleration is stored inthe auxiliary power source 3, the State of Charge (SOC), which is anavailable capacity of a battery expressed as a percentage of its ratedcapacity, of the auxiliary power source 3 becomes higher than that ofthe main power source 2. Thus, the voltage of the auxiliary power source3 is higher, and therefore the regenerative electric power can besupplied from the auxiliary power source 3 to the ordinary loads bysimply closing the switch 6.

Second Embodiment

Next, as a second embodiment, a power supply control operation forcontrolling supply of power from the generator 1 or the auxiliary powersource 3 to the main power source 2 will be described with reference toa flowchart shown in FIG. 4. This is a method in which the charge levelof the auxiliary power source 3 is sensed and is used for the powersupply control operation.

At step 20, it is determined whether the output capability of the DC/DCconverter 4 is greater than the total power consumption of all of theelectrical loads (this will be referred to as an overall load value),and the charge capacity per unit time of the auxiliary power source 3 isgreater than the overall load value. When the determination result isYES, control proceeds to step 21. In contrast, when the determinationresult is NO, control proceeds to step 22. At step 21, since there isthe surplus in the charge capacity of the auxiliary power source 3 withrespect to the overall load value, and there is also the surplus in theoutput capability of the DC/DC converter 4, the power generation by thegenerator 1 is cut off, and electric power is supplied from theauxiliary power source 3 to the main power source 2 through the firstsupply circuit 5 having the DC/DC converter 4 (first control state).

At step 22, it is determined whether the output capability of the DC/DCconverter 4 is below the overall load value, and furthermore thecapacity per unit time of the auxiliary power source 3 is greater thanthe overall load value, or alternatively the temperature of the DC/DCconverter 4 is higher than a fixed value. When the determination resultis YES, control proceeds to step 23. In contrast, when the determinationresult is NO, control proceeds to step 24. At step 23, since there isthe surplus in the charge capacity of the auxiliary power source 3 withrespect to the overall load value, but there is no surplus in the outputcapability of the DC/DC converter 4 (or alternatively, the temperatureof the DC/DC converter 4 is high), power generation by the generator 1is cut off, and electric power is supplied from the auxiliary powersource 3 to the main power source 2 through the first supply circuit 5and the second supply circuit 7 (shown as a switch circuit in thefigure) (third control state).

At step 24, it is determined whether the output capability of the DC/DCconverter 4 is equal to or below the overall load value, and furthermorethe capacity per unit time of the auxiliary power source 3 is equal toor below the overall load value. When the determination result is YES,control proceeds to step 25. In contrast, when it is NO, controlproceeds to step 26. At step 25, since there is no surplus in the chargecapacity of the auxiliary power source 3 with respect to the overallload value, and furthermore there is no surplus in the output capabilityof the DC/DC converter 4 (but, the temperature of the DC/DC converter 4is equal to or below a fixed value), power generation (at a Lo level) bythe generator 1 is carried out, and electric power is supplied from thegenerator 1 to the main power source 2 through the first supply circuit5 and the second supply circuit 7 (third control state).

At step 26, it is determined whether the temperature of the DC/DCconverter 4 is higher than a fixed value, or the auxiliary power source3 capacity is higher than a fixed value. When the determination resultis YES, control proceeds to step 27. In contrast, when it is NO, controlproceeds to step 28. At step 27, to prevent heat-induced failure of theDC/DC converter 4, and to prevent overcharging of the auxiliary powersource 3, electric power is supplied from the generator 1 to the mainpower source 2 using the second supply circuit 7 only (second controlstate). At this time, the power generation level (Lo) of the generator 1is a level, at which power supply that corresponds to the ordinary loads8 b is possible even if the auxiliary power source 3 is fully charged.

At step 28, it is determined whether the charge capacity of theauxiliary power source 3 is within a first corresponding predeterminedrange (e.g., between 40% and 50%). When the determination result is YES,control proceeds to step 29. In contrast, when the determination resultis NO, control proceeds to step 30. At step 29, since the chargecapacity of the auxiliary power source 3 is low, the generating capacityof the generator 1 is raised (to a Hi level. The Lo and Hi levels arerelative terms. That is, the Lo level is used to express a relativelylow power generation level of the generator, and the Hi level is used toexpress a relatively high power generation level of the generator, whichis higher than the Lo level). Also, when high loads, which consume alarge amount of electric power, have been turned on, an idle speed isincreased by a predetermined amount (first idle increase).

At step 30, it is determined whether the charge capacity of theauxiliary power source 3 is within a second corresponding predeterminedrange (e.g., between 30% to 40%). When the determination result is YES,control proceeds to step 31. In contrast, when the determination resultis NO, control proceeds to step 32. At step 31, since the chargecapacity of the auxiliary power source 3 is low, or the charge capacityof the auxiliary power source 3 is not increased even though the powergeneration capacity of the generator 1 has been increased, the firstidle increase is carried out, and also the supply of power to theordinary loads 8 b is cut off (or limited). When the high load, which isamong the ordinary loads 8 b and consumes a large amount of electricpower, has been turned on, the idle speed is increased further by apredetermined amount (second idle increase). In contrast, at step 32,abnormality (failure) of the auxiliary power source 3 is reported, i.e.,is warned to the driver (e.g., asking the driver to evacuate to a safeplace, or guiding the vehicle along a route to an automobile dealerthrough use of, for example, a navigation system).

According to the second embodiment, when the output capability of theDC/DC converter 4 is equal to or below the overall load value, theswitch 6 is switched on, and the second supply circuit 7 is used. Inthis way, it is possible to supply electric power from the generator 1or the auxiliary power source 3 to the main power source 2 even at thetime of shortage of the supply of electric power from the DC/DCconverter 4 or at the time of failure of the DC/DC converter 4.

When the temperature of the DC/DC converter 4 has become higher than thefixed value, the supply capability of the DC/DC converter 4 is limited,or the switch 6 is switched on, and only the second supply circuit 7 isused. In this way, the heat-induced failure of the DC/DC converter 4 canbe limited. Thus, as discussed above, the second supply circuit 7, whichhas the switch 6, is provided between the auxiliary power source 3 andthe main power source 2 in parallel with the first supply circuit 5,which has the DC/DC converter 4. In this way, it is possible to reducethe capacity and the size of the DC/DC converter 4.

Also, as discussed with reference to step 27, even in the fully chargedstate of the auxiliary power source 3, the power generation level (Lo)of the generator 1 is kept to a level which enables the supply ofelectric power in the amount that corresponds to the ordinary loads 8 b.In this way, the power is supplied from the generator 1 to the ordinaryloads 8 b instead of charging the auxiliary power source 3 during thedeceleration of the vehicle. For example, on a long downward slope, evenafter the amount of regenerative electric power is stored in theauxiliary power source 3 (the fully charged state), the regenerativeelectric power is consumed by the ordinary loads 8 b. Thus, theregenerative electric power can be used effectively.

The control operation of the second embodiment can be used irrespectiveof which of the main power source 2 and the auxiliary power source 3 hasthe higher output voltage (nominal voltage). That is, it can be used inthe case where the output voltage (nominal voltage) of the main powersource 2 is higher than that of the auxiliary power source 3, or in thecase where the output voltage (nominal voltage) of the auxiliary powersource 3 is higher than that of the main power source 2.

Third Embodiment

Next, as a third embodiment, a control operation of the generator 1 willbe described with reference to a flowchart shown in FIG. 5. In thismethod, the control operation is carried out based on the power sourcevoltages only without using a sensing means of a State of Charge (SOC).

At step 40, it is determined whether the output voltage V1 of theauxiliary power source 3 is equal to or above a fixed value (e.g., 12V). When the determination result is YES, control proceeds to step 44.In contrast, when the determination result is NO, control proceeds tostep 42. At step 44, it is determined whether the vehicle isdecelerating. When the determination result at step 44 is NO, controlproceeds to step 41. At step 41, since there is the surplus in thecharge capacity of the auxiliary power source 3, power generation by thegenerator 1 is cut off, and electric power is supplied from theauxiliary power source 3 to the main power source 2 through the firstsupply circuit 5 (the DC/DC converter 4) (first control state).

At step 42, it is determined whether the vehicle is decelerating. Whenthe determination result is YES, control proceeds to step 43. Incontrast, when the determination result is NO, control proceeds to step46. At step 43, regenerative electric power, which is generated by thegenerator 1, is recovered into the auxiliary power source 3, andelectric power is also supplied to the main power source 2 through thefirst supply circuit 5 (first control state).

Returning to step 44, when the determination result is YES, controlproceeds to step 45. At step 45, since the output voltage V1 of theauxiliary power source 3 is larger than the fixed value although thevehicle is in the decelerating state, regenerative electric power (Lolevel), which is generated by the generator 1, is supplied to the mainpower source 2 through the first supply circuit 5 and the second supplycircuit 7 (shown as a switch in the figure) (third control state).Alternatively, electric power is supplied to the main power source 2through one the first supply circuit 5 and the second supply circuit 7.In this way, power supply, which corresponds to the ordinary loads 8 b,is effected even in the fully charged state of the auxiliary powersource 3, and it is possible to realize regeneration on deceleration bysupplying power to the ordinary loads 8 b instead of by charging.

At step 46, it is determined whether the vehicle is in the steadytraveling state or in the accelerating state, and furthermore, whetherthe output voltage V2 of the DC/DC converter 4 is within a predeterminedrange (e.g., between 12.5 V and 13 V). When the determination result isYES, control proceeds to step 47. In contrast, when the determinationresult is NO, control proceeds to step 48. At step 47, the supplycapability of the DC/DC converter 4 is increased, and electric power issupplied from the generator 1 to the main power source 2 through thefirst supply circuit 5 (first control state). This corresponds to thestate where the charge level of the main power source 2 is reduced, andthe output instruction to the DC/DC converter 4 is insufficient. Thus,in such a case, to counteract against this situation, the output of theDC/DC converter 4 is increased, and the charge level of the main powersource 2 is kept to a relatively high level, so that deterioration ofthe main power source 2 caused by electrical discharge is limited.

At step 48, it is determined whether the temperature of the DC/DCconverter 4 is greater than a fixed value, or whether the output voltageV1 of the auxiliary power source 3 is within a predetermined range(e.g., between 11 V and 12 V). When the determination result is YES,control proceeds to step 49. In contrast, when the determination resultis NO, control proceeds to step 50. At step 49, the generator 1 iscontrolled to always generate electric power (Lo level), and electricpower is supplied from the generator 1 to the main power source 2through the second supply circuit 7 (second control state). This isperformed to limit temperature increase of the DC/DC converter 4.

At step 50, it is determined whether the output voltage V1 of theauxiliary power source 3 is smaller than a fixed value (e.g., 11 V), andfurthermore the output voltage V2 of the DC/DC converter 4 is within apredetermined range (e.g., between 12 V and 12.5 V). When thedetermination result is YES, control proceeds to step 51. In contrast,when the determination result is NO, control proceeds to step 52. Atstep 51, the first idle increase is carried out to increase the idlespeed, and the supply of power to the ordinary loads 8 b is cut off (orlimited) since the charge capacity of the auxiliary power source 3 islow, and the output voltage V2 of the DC/DC converter 4 is also low eventhough the generator 1 is generating (at the Lo level). Furthermore,when the high load, which is among the ordinary loads 8 b and whichconsumes a large amount of electric power, is turned on, the second idleincrease is carried out to raise the idle speed further. Here, since thegenerated power level is low, and the supply of electric power from theDC/DC converter 4 cannot keep up, the idle increase is carried out tocorrespond with this situation. At step 52, the driver is notified,i.e., is warned about an abnormality of the power supply system S (thesame as step 32).

According to the third embodiment, the output of the generator 1 can beeffectively controlled according to the output voltage V1 of theauxiliary power source 3 and the output voltage V2 of the DC/DCconverter 4.

Furthermore, since the generator 1 is connected to the high-performanceauxiliary power source 3, the charge acceptance of which is higher thanthat of the main power source 2 and which allows easy detection of itsoperational state with high accuracy, it is possible to recoverregenerative electric power generated by the generator 1 to theauxiliary power source 3 with good efficiency during the deceleration ofthe vehicle. That is, in order to recover a large amount of regenerativeenergy in the short time of deceleration, it is important to have arelatively large difference between the voltage of the generator 1 andthe voltage of the power source (e.g., the voltage of the auxiliarypower source 3).

However, in the case (e.g., the case of the main power source 2, thecharge acceptance of which is lower than that of the auxiliary powersource 3) where the difference between the voltage of the generator 1and the voltage of the power source is relatively small, and theinternal resistance of the power source is relatively large, the powersource 2 is not charged to an acceptable SOC within a predetermineddeceleration time A, as shown in FIG. 6( b). In such a case, the powersource cannot be charged sufficiently. Furthermore, when the differencebetween the voltage of the generator 1 and the voltage of the powersource becomes excessively large, overshooting beyond the acceptable SOCoccurs, as shown in FIG. 6( c). In such a situation, in the highperformance battery, such as the auxiliary power source 3 (Li ionbattery), heat production becomes large, and performance may bedeteriorated due to increased internal resistance and so on.

In contrast, in the power supply system S, since the output voltage ofthe auxiliary power source 3, which recovers regenerative electric powerduring the deceleration of the vehicle, is smaller than that of the mainpower source 2 and the internal resistance of the auxiliary power source3 is also small, the charge acceptance capability of the auxiliary powersource 3 is good. Thus, as shown in FIG. 6( a), it is possible torecover a large amount of regenerative energy in the predetermineddeceleration time A. As a result, it is possible to carry out maximumregenerative charging from the generator 1 to the auxiliary power source3 within a short time of deceleration. Also, through the cutting of thepower generation of the generator 1 in the steady traveling state or inthe accelerating state, the load on the engine is reduced, therebycontributing to a reduction in the fuel consumption.

In the third embodiment, there is described the case where the outputvoltage (nominal voltage) of the auxiliary power source 3 is lower thanthat of the main power source 2. However, the same control operation canalso be applied to a case where the auxiliary power source 3 has ahigher output voltage (nominal voltage) over the main power source 2.However, since the output voltage of the auxiliary power source 3becomes higher, the voltage determination values of the respective steps(S40, S42, S44, S48, S50 in FIG. 5) used in the determination of theoutput voltage V1 of the auxiliary power source 3 need to be changedaccordingly. For example, the voltage determination values, which areused in the case where the output voltage (nominal voltage) of theauxiliary power source 3 is set to be 14.4 V, are shown in the flowchartof FIG. 7 (S40 a, S42 a, S44 a, S48 a, S50 a).

Fourth Embodiment

Next, as a fourth embodiment, a control operation in a case where theoutput voltage of the auxiliary power source 3 is higher than that ofthe main power source 2, will be described with reference to a flowchartshown in FIG. 8.

At step 60, it is determined whether the output voltage of the auxiliarypower source 3 is higher than that of the main power source 2. When thedetermination result is NO (i.e. auxiliary power source voltage≦mainpower source voltage), control proceeds to step 61. In contrast, whenthe determination result is YES, control proceeds to step 62. At step61, power generation is carried out by the generator 1, and theauxiliary power source 3 is charged. This process is continued until theoutput voltage of the auxiliary power source 3 becomes higher than thatof the main power source 2.

At step 62, it is determined whether the level of electric power, whichis supplied from the auxiliary power source 3 to the main power source 2and the ordinary loads 8 b, is above a predetermined value. When thedetermination result is NO, control proceeds to step 63. In contrast,when the determination result is YES, control proceeds, to step 64. Atstep 63, the first control state is selected. That is, the DC/DCconverter 4 is driven (ON), and the switch 6 is opened (OFF). Thus, therequired power is supplied from the auxiliary power source 3 to the mainpower source 2 and the ordinary loads 8 b through the first supplycircuit 5. In this control operation, for example, the voltage of theoutput side of the DC/DC converter 4 is controlled to have a fixedvalue. After that, control proceeds to step 65. In contrast, at step 64,the large amount of electric power needs to be supplied, so that theelectric power is supplied at the maximum output of the DC/DC converter4 (shortage of the electric power being compensated through dischargefrom the main power source 2).

At step 65, it is determined whether the output voltage of the auxiliarypower source 3 is equal to or below the acceptable rated voltage of theordinary loads 8 b. When the determination result is YES, controlproceeds to step 66. In contrast, when the determination result is NO,control returns to step 62. At step 66, the second control state isselected. That is, the DC/DC converter 4 is stopped (OFF), and theswitch 6 is closed (ON). Thus, the electric power is supplied from theauxiliary power source 3 to the main power source 2 and the ordinaryloads 8 b through the second supply circuit 7.

According to the control operation of the fourth embodiment, anexcessive voltage is not applied to the ordinary loads 8 b, such as thelights, and therefore a reduction in the lifetime of the ordinary loads8 b can be limited. Furthermore, in the case where the output voltage ofthe auxiliary power source 3 has fallen to or below the acceptable ratedvoltage of the ordinary loads 8 b, the path is shifted from the DC/DCconverter 4 to the switch 6. Therefore, a loss associated with the DC/DCconverter is eliminated, and thereby effective power supply can beimplemented.

Fifth Embodiment

Next, as a fifth embodiment, a control operation performed at the timeof switching from the first control state to the second control state orat the time of switching from the second control state to the firstcontrol state will be described with reference to a flowchart of FIG. 9.

At step 70, a switch command for switching the control state is issued.Specifically, switch command is a command for switching from the firstcontrol state to the second control state or a command for switchingfrom the second control state to the first control state. At step 71, itis determined whether the voltage difference between the main powersource 2 and the auxiliary power source 3 is greater than apredetermined value. When the determination result is YES, controlproceeds to step 72. In contrast, when the determination result is NO,control jumps to step 73.

At step 72, the ECU 17 (serving as a first control means) controls theoutput voltage of the DC/DC converter 4. More specifically, at step 72,the output voltage of the DC/DC converter 4 is increased to a higher oneof the voltage of the main power source 2 and the voltage of theauxiliary power source 3 or is decreased to a lower one of the voltageof the main power source 2 and the voltage of the auxiliary power source3. Thereafter, control returns to step 71. At step 73, the secondcontrol state (or the first control state) is selected since the voltagedifference between the main power source 2 and the auxiliary powersource 3 is smaller than the predetermined value.

According to the control operation of the fifth embodiment, the voltagefluctuations at the time of switching the control state (e.g., at thetime of switching on of the switch 6 provided in the second supplycircuit 7) are limited, so that, for example, flickering of the lightscan be limited.

Sixth Embodiment

Next, as a sixth embodiment, a control operation at the time ofswitching from the second control state to the third control state(i.e., at the time of supplying electric power through use of both theDC/DC converter 4 and the switch 6) will be described with reference toa flowchart shown in FIG. 10.

At step 80, the second control state is selected. That is, the switch 6is closed (ON), and electric power is supplied through the second supplycircuit 7. At step 81, it is determined whether the temperature of theswitch 6 is increased beyond a predetermined value. When thedetermination result is YES, control proceeds to the following step 82.In contrast, when the determination result is NO, control returns tostep 80.

At step 82, the DC/DC converter 4 is driven (ON), and the control stateis switched to the third control state. That is, power supply is carriedout using both the first supply circuit 5 and the second supply circuit7.

According to the sixth embodiment, when the temperature of the switch 6is increased beyond the predetermined value, electric power is suppliedthrough the second supply circuit 7, which has the switch 6, and alsothrough the first supply circuit 5, which has the DC/DC converter 4.Thus, the heat generation of the switch 6 can be limited.

Seventh Embodiment

FIG. 11 is an electrical circuit diagram of a power supply system Saccording to a seventh embodiment. In the power supply system S of theseventh embodiment, as shown in FIG. 11, an auxiliary power sourceswitch 19 (e.g., a relay switch) is connected to the anode side of theauxiliary power source 3, and the auxiliary power source switch 19 iscontrolled by the system ECU 17.

With this construction, for example, when the auxiliary power source 3fails, the auxiliary power source switch 19 is switched off at the timeof evacuating the vehicle to a safe place or at the time of driving thevehicle to an automobile dealer. Thus, the auxiliary power source 3 iselectrically isolated from the power system S. As a result, the safetyof the power supply system S is ensured.

In the case where electrical loads, which consume a relatively largeamount of electric power among ordinary loads 8 b, are operated, theauxiliary power source switch 19 may be switched off to reliably supplythe electric power from the generator 1 to the main power source 2 andthe ordinary loads 8 b. This is true even when the electric power issupplied from the generator 1 through the first supply circuit 5 orthrough the second supply circuit 7 or through both the first and secondsupply circuits 5, 7.

Also, in a case where the vehicle is equipped with an idle stop device,which automatically stops the engine when the vehicle has stopped, forexample, at a red traffic light at an intersection, the auxiliary powerswitch 19 may be turned off at the time of stopping the engine, forexample, at the red traffic light to effectively enable the next enginestart (restarting after the automatic stop). By turning off theauxiliary power source switch 19, the required electrical capacity thatis required for the restarting of the engine can be ensured at the timeof restarting the engine.

Also, when rapid charging is carried out on the deceleration of thevehicle in the state where the 100% capacity voltage of the auxiliarypower source 3 is smaller than the output voltage of the generator 1,the auxiliary power source switch 19 may be turned off. In this way, ina case of encountering a failure, such as control failure of the powergeneration, the excessive charging of the auxiliary power source 3 canbe cut by turning off the auxiliary power switch 19.

The auxiliary power source switch 19 may be alternatively connected tothe cathode side of the auxiliary power source 3, as shown in FIG. 12 orFIG. 13. In the example shown in FIG. 13, the auxiliary power sourceswitch 19 is disposed between the generator 1 and the auxiliary powersource 3 on the generator 1 side of the input side connection point B ofthe DC/DC converter 4.

Eighth Embodiment

FIG. 14 is an electrical circuit diagram of a power supply system Saccording to an eighth embodiment. In the power supply system S of theeighth embodiment, as shown in FIG. 14, a capacitor 20 is connected tothe output side (the main power source 2 side) of the DC/DC converter 4of the first supply circuit 5. When a relatively large power is suppliedfrom the DC/DC converter 4 to the main power source 2, the capacitor 20smoothes the voltage. In this way, it is possible to supply a morestable voltage to the main power source 2 through the DC/DC converter 4.

Ninth Embodiment

FIG. 15 is an electrical circuit diagram of a power supply system Saccording to a ninth embodiment. In the power supply system S of theninth embodiment, as shown in FIG. 15, the charge acceptance capabilityof the main power source 2 is sensed by monitoring the output voltage ofthe main power source 2 with a voltmeter 21 or the like. In this way,detecting the charge acceptance capability of the main power source 2with a sensor (e.g., a sensor for sensing the current, the voltage, orthe temperature), so a low-cost system can be realized.

Tenth Embodiment

FIG. 16 is an electrical circuit diagram of a power supply system Saccording to a tenth embodiment. In the power supply system S of thetenth embodiment, as shown in FIG. 16, electrical loads 22 (e.g., adefogger, a seat heater), which tolerate voltage fluctuations and do notrequire a dark current, are connected to the auxiliary power source 3and the generator 1 through a relay 23 rather than connecting to themain power source 2. The electrical load, which does not require thedark current, may be one of an electrical load, such as an ECU that doesnot have an internal memory, and an electrical load, such as an ECU thatalways uses an initial constant of an internal memory. A controller 24(an ECU), which opens and closes the relay 23, is connected to the mainpower source 2 and receives a power supply from the main power source 2.

In this way, the power source (the dark current) only to the resettableloads (i.e., loads that can be properly reset even upon a powerinterruption) can be cut to limit complete discharging of the battery 2,which occurs, for example, over a time during which the vehicle isparked for an extended period (e.g., weeks, months or years), or over atime of unintentionally leaving the vehicle door open to cause the lampin the vehicle to be turned and left on for hours or days. Thereby, thedeterioration of the lifetime of the main power source 2 and thedeterioration of the performance of the main power source 2 can belimited. Furthermore, the electrical loads 22, which do not require thedark current, can receive electric power from the auxiliary power source3 or the generator 1. The means for cutting off the dark current (darkcurrent blocking means of the present invention) may include thefollowing, i.e., a) a means having a timer function for cutting off adark current after fixed time; b) a means for sensing the capacity ofthe auxiliary power source 3; c) a means for receiving an externalcommunication signal; d) a means for sensing termination of signaltransmission or signal reception at a radio transmitter; and e) aswitch, such as a touch panel switch at an exterior of the vehicle.

Eleventh Embodiment

FIG. 17 is an electrical circuit diagram of a power supply system Saccording to an eleventh embodiment. In the power supply system S of theeleventh embodiment, a bypass circuit 25, which is connected to thefourth supply circuit 12 while bypassing the auxiliary power sourceswitch 19, is provided to the circuit of FIG. 13, which includes theauxiliary power switch 19.

In this way, even in the case where the auxiliary power source switch 19is turned off, electric power can be supplied from the main power source2 or the auxiliary power source 3 to the safety ECU 16. Thus, theredundant system is provided to the safety ECU 16, which is involved inthe travel safety.

Twelfth Embodiment

FIG. 18 is an electrical circuit diagram of a power supply system Saccording to a twelfth embodiment. The power supply system S of thetwelfth embodiment is implemented by modifying, for example, the circuitdiagram (see FIG. 15) of the ninth embodiment in such a manner that avoltage stabilizer 26 is provided to the fourth supply circuit 12. Inthis way, the minimum guaranteed voltage can be reliably supplied to thesystem ECU 17, which is an important load.

(Variations)

In the first embodiment, the two power sources (the main power source 2and the auxiliary power source 3), which are used in the power supplysystem S of the first aspect of the present application, are describedsuch that the nominal voltage (or the nominal capacity) of the mainpower source 2 is higher than that of the auxiliary power source 3.However, alternative to this construction, the nominal voltage (or thenominal capacity) of the auxiliary power source 3 may be higher thanthat of the main power source 2. Further alternatively, the main powersource 2 and the auxiliary power source 3 may have a common operationalrange, in which a working voltage of the main power source 2 coincideswith a working voltage of the auxiliary power source 3.

In the first embodiment, the Pb battery and the Li ion battery aredescribed as examples of the main power source 2 and the auxiliary powersource 3, respectively. However, the present invention is not limited tothis. For example, besides the Pb battery, the main power source 2 maybe a Li ion battery or a Ni hydrogen battery. Also, besides the Li ionbattery, the auxiliary power source 3 may be a Pb battery, a Ni hydrogenbattery or an electrical double-layer capacitor.

Furthermore, in the first embodiment, the alternator is used as thegenerator 1. Alternative to the alternator, a motor generator, which hasa power generating function, may be used. Furthermore, the generator 1does not have to be belt-driven by the engine. For example, thegenerator 1 may alternatively be connected to a wheel axle or acrankshaft through a transmitting means, such as a gear or a belt.Further alternatively, the generator 1 may be directly connected to thewheel axle or the crankshaft. Further alternatively, a heat-regeneratinggenerator, which is capable of generating electric power by convertingthermal energy into kinetic energy, may be used. Also, a thermoelectricdevice, which is capable of directly converting thermal energy intoelectrical energy, may be used.

Thirteenth Embodiment

Next, a vehicle power supply system of a thirteenth embodiment accordingto a second aspect of the present application will be described. FIG. 19is an overall view of an engine starting system (which will be referredto as a main system) to which the vehicle power supply system accordingto the thirteenth embodiment is applied. FIG. 20 is a circuit diagram ofthe vehicle power supply system.

The present system is mounted on the vehicle, which has an idle stopfunction. Furthermore, as shown in FIG. 19, the present system includesa starting device (discussed below), an alternator 102 (a generatingmeans of the present invention), an engine ECU 103, an idle stop ECU 104and two batteries 105, 106. The starting device starts an engine 101.The alternator 102 (generating means of the invention) is driven by theengine 101 to generation electric power. The engine ECU 103 controls anoperational state of the engine 101. The idle stop ECU 104 controls theidle stop function.

The idle stop function is a function for automatically stopping theengine 101, for example, at the time of stopping the vehicle at anintersection and then automatically restarting the engine 101 at thetime of satisfying an engine start condition (e.g., at the time ofremoving a foot of a driver from a brake pedal).

The starting device includes a starter 107 of a belt type and a starter108 of a gear type. The starter 107 of the belt type is given the higherpriority than the starter 108 of the gear type. The starter 108 of thegear type is used in a case where the engine start operation, which iscarried out by the starter 107 of the belt type, is out of apredetermined state, for example, at the time of malfunctioning of thestarter 107, the engine 101 or the belt.

In the starter 107 of the belt type, a starter pulley 107 a, which isattached to the output shaft of the motor, is connected to a crankpulley 101 a, which is attached to the crankshaft of the engine 101,through a belt 109, and the rotational force of the motor is conductedto the crank pulley 101 a through the belt 109 to start the engine.

In the starter 108 of the gear type, for example, a pinion gear (notshown) is meshed with a ring gear (not shown) of the engine 101, andthen the rotational force of the motor is conducted from the pinion gearto the ring gear to start the engine.

Similar to the starter 107 of the belt type, in the alternator 102, apulley 102 a of the alternator 102 and the crank pulley 101 a are alwaysconnected to each other through the belt 109.

The engine ECU 103 calculates fuel injection quantities and ignitiontimings to obtain an optimal air/fuel ratio in the engine 101. Theengine ECU 103 electronically controls an EFI (Electronic Fuel Injectionapparatus) 110 based on the result of the calculations. Various sensors(not shown) for sensing the running state of the engine 101, the batterystate and the external air temperature are connected to the engine ECU103. Information, which is required to control the engine, is inputtedfrom these sensors. The information include, for example, the vehiclespeed, the engine rotational angle signal, the accelerator openingdegree, the engine coolant temperature, the battery states, thevoltages, the currents, the temperatures, and the external airtemperature.

When a predetermined engine stop condition is satisfied (e.g., thevehicle speed is 0 km/h and the brake pedal is pressed), the idle stopECU 104 outputs an engine stop signal (a fuel cutoff signal and anignition cutoff signal) to the engine ECU 103. When the above-mentionedengine start condition is satisfied, the idle stop ECU 104 outputs anengine start signal (a fuel injection signal and an ignition signal) tothe engine ECU 103. Furthermore, when an abnormality is sensed in theengine start operation performed by the starter 107 of the belt type,the starter 107 of the belt type is switched to the starter 108 of thegear type.

The two batteries 105, 106 include a high-performance main battery 105(e.g., a Li ion battery, a nickel type battery or an electricaldouble-layer capacitor) and a sub-battery 106 having better dischargecharacteristics at low temperatures over the main battery 105 (e.g., alead battery). The term “High-performance” means superior with respectto some of the following points (1) to (6). These points (1) to (6)include (1) energy density, (2) output density, (3) cycle life, (4)battery state detectability (SOC, HOC etc.), (5) discharge depth and (6)charge acceptance capability.

Next, the circuit construction of the vehicle power supply system and amethod of using the batteries 105, 106 will be described with referenceto FIG. 20.

In the vehicle power supply system of the thirteenth embodiment,regenerative energy, which is generated by the alternator 102 duringdeceleration of the vehicle, is recovered to the main battery 105. Then,the sub-battery 106 is charged with a micro current from this mainbattery 105 through, for example, a DC/DC converter 111. This chargingof the sub-battery 106 from the main battery 105 is carried out when thevoltage difference between the main battery 105 and the sub-battery 106is smaller than a predetermined value, or when the power generation ofthe alternator 102 is stopped. In place of the DC/DC converter 111, arelay switch 112 shown in FIG. 20 may be provided. Charging may bestarted when this relay switch 112 is turned on.

The main battery 105 is used mainly for the following purposes (a) to(d), i.e., (a) supplying power to ordinary electrical loads 13 mountedon the vehicle; (b) supplying power to the starter 107 when the enginetemperature (or a battery temperature) during the engine start operationis in a normal range (discussed below); (c) supplying power toelectrical loads 114, which require a voltage guarantee (e.g., a brakingsystem, a steering system, a navigation system), at the time ofsupplying power from the sub-battery 106 to the starter 107; and (d)supplying power (supplying dark currents) to the ordinary electricalloads 113 after the engine is stopped by turning off of the IG key.

The sub-battery 106 is mainly used for the following purposes (e) and(f), i.e., (e) supplying power to the starter 107 when the enginetemperature during the engine start operation is in an extremely lowtemperature range, a low temperature range or a high temperature range(discussed below); and (b) supplying power to the electrical loads 114,which require a guaranteed voltage, at the time of supplying power fromthe main battery 105 to the starter 107.

A starter power supply circuit 115, which is connected to the starter107, includes a starter power supply shift switch 116 and a relay switch117. The starter power supply shift switch 116 switches between the mainbattery 105 and the sub-battery 105 to connect it to the starter 107.The relay switch 117 is turned on at the time of using both thesub-battery 106 and the main battery 105.

A power supply circuit 118, which is connected to the electrical loads114 that require a guaranteed voltage, include a power supply shiftswitch 119, which switches between the main battery 105 and thesub-battery 106.

A short circuit 121, which includes a relay switch 120, is arrangedbetween the main battery 105 and the electrical loads 114 to providestable supply of power to the electrical loads 114, which require theguaranteed voltage, at the time of switching between the main battery105 and the sub-battery 106.

Now, the battery switching control operation carried out during theengine start operation will be described. FIG. 21 is a flowchart showinga battery switching control procedure.

At step 110, the engine temperature is sensed. Here, it should be notedthat an engine temperature related temperature (e.g., a batterytemperature), which correlates with the engine temperature, can besensed in place of the engine temperature.

At step 120 and step 130, the sensed engine temperature is compared withpredetermined temperatures. Here, temperature ranges of predeterminedtemperatures T1, T2 and T3 (where T1<T2<T3) are defined as follows. Thatis, the temperature range below T1 is an extremely low temperaturerange. The temperature range between T1 and T2 is a low temperaturerange. The temperature range between T2 and T3 is a normal temperaturerange. The temperature range above T3 is a high temperature range.

Specifically, at step 120, it is determined whether the sensed enginetemperature is below the predetermined temperature T1 (i.e., in theextremely low temperature range) or above the predetermined temperatureT3 (i.e. in the high temperature range). When this determination resultis YES, control proceeds to step 160. Alternatively, when thedetermination result is NO, control proceeds to step 130. At step 130,it is determined whether the sensed engine temperature is lower than thepredetermined temperature T2 (i.e., in the low temperature range). Whenthis determination result is YES, control proceeds to step 150.Alternatively, when the determination result is NO, control proceeds tostep 140.

At step 140 (in the case where it is determined that the enginetemperature is in the normal temperature range), the following steps 141to 144 are executed. First, at step 141, the power supply shift switch119 is switched to the sub-battery 106 side (the position shown with adotted line in FIG. 20), and power is supplied from the sub-battery 106to the electrical loads 114, which require a guaranteed voltage.

Then, at step 142, the starter power supply shift switch 116 is switchedto the main battery 105 side (the position shown with a solid line inFIG. 20), and start-up electric power is supplied from the main battery105 to the starter 107. At this time, the relay switch 117 is in its OFFstate.

At step 143, the starter 107 is turned on. At step 144, it is determinedwhether the engine start operation has completed. When the result ofthis determination is YES (the engine start operation has completed),control proceeds to step 170. In contrast, when the determination resultis NO, control proceeds to step 152.

At step 150 (in the case where it is determined that the enginetemperature is in the low temperature range), the following steps 151 to154 are executed. First, at step 151, the power supply shift switch 119is switched to the main battery 105 side (the position shown with thesolid line in FIG. 20), and power is supplied from the main battery 105to the electrical loads 114, which require the guaranteed voltage.

Then, at step 152, the starter power supply shift switch 116 is switchedto the sub-battery 106 side (the position shown with the dotted line inFIG. 20), and start-up electric power is supplied from the sub-battery106 to the starter 107. At this time, the relay switch 117 is in its OFFstate.

Then, at step 153, the starter 107 is turned on. At step 154, it isdetermined whether the engine start operation has completed. When theresult of this determination is YES, control proceeds to step 170. Incontrast, when the determination result is NO, control proceeds to step160.

At step 160 (in the case where it is determined that the enginetemperature is in the extremely low temperature range or the hightemperature range), the following steps 161 to 163 are executed. First,at step 161, the starter power supply shift switch 116 is switched tothe main battery 105 side, and the relay switch 117 is turned on. As aresult, start-up electric power is supplied from both the main battery105 and the sub-battery 106 to the starter 107.

At step 162, the starter 107 is turned on. At step 163, it is determinedwhether the engine start operation has completed. When the determinationresult is YES (the engine start operation has completed), controlproceeds to step 170. In contrast, when the determination result is NO,control proceeds to step 190.

At step 170, the electric power to the starter 107 is turned off. Atstep 180, the power supply shift switch 119 is switched to the mainbattery 105 side, and power is supplied from the main battery 105 to theelectrical loads 114, which require a guaranteed voltage. Then, thepresent operation is terminated. At step 190, the electric power to thestarter 107 is turned off. At step 200, an abnormality warning isoutputted, and the present control operation is terminated.

With the battery switching control operation described above, incorrespondence with the engine temperature at the time of starting theengine, one of the main battery 105 and the sub-battery 106 is selected,or alternatively both the batteries 105, 106 are used together to supplypower to the starter 107. Thus, the main battery 105 and the sub-battery106 can be used effectively in accordance with their respectivecharacteristics.

The circuit diagram shown in FIG. 20 is constructed in such a mannerthat the main battery 105 and the sub-battery 106 are connected to thestarter 107 in parallel at the time of supplying electric power fromboth the main battery 105 and the sub-battery 106 to the starter 107.Alternatively, the circuit may be constructed in such a manner that themain battery 105 and the sub-battery 106 are connected in series.

When start-up electric power is supplied from the main battery 105 tothe starter 107, electric power is supplied from the sub-battery 106 tothe electrical loads 114, which require the guaranteed voltage. Whenstart-up electric power is supplied from the sub-battery 106 to thestarter 107, electric power is supplied from the main battery 105 to theelectrical loads 114, which require the guaranteed voltage.Consequently, the required voltage can be supplied in a stable manner tothe electrical loads 114, which require the guaranteed voltage, withoutbeing influenced by voltage drop of each battery 105, 106, which occursat the time of supplying electric power to the starter 107.

Next, a control method for charging the sub-battery 106 from the mainbattery 105 will be described with reference to a flowchart shown inFIG. 22. Charging of the sub-battery 106 from the main battery 105 isexecuted in the state where the engine is stopped.

At step 300, the temperature, which is used to determine whether thecharging needs to be initiated, is sensed. Here, a battery temperature,the engine temperature, or an external air temperature can be used asthis temperature. At step 310, it is determined whether the sensedtemperature is smaller than a predetermined value “a”. When the resultof this determination is YES, control proceeds to step 320. In contrast,when the determination result is NO, control returns to step 300.

At step 320, it is determined whether the charge state of the mainbattery 105 and the charge state of the sub-battery 106 are below apredetermined state “b”. here, the charge state of the main battery 105is determined based on measuring of SOC, a state of health (SOH), andthe charge state of the sub-battery 106 is determined based on a voltagevalue. When the determination result is YES, control proceeds to step330. In contrast, when the determination result is NO, control return tostep 300.

At step 330, charging from the main battery 105 to the sub-battery 106is started. At step 340, it is determined whether the charge state ofthe main battery 105 and the charge state of the sub-battery 106 arehigher than the predetermined state “b”. When the result of thisdetermination is YES, the present control operation is terminated. Incontrast, when the result of this determination is NO, control returnsto step 330.

An additional operational sequence may be inserted in theabove-described flowchart. That is, in the additional operationalsequence, a temperature gradient may be monitored, and the chargingcurrent may be determined based on the temperature gradient.

Furthermore, as shown in FIG. 20, a current sensor 122 may be insertedin the power supply line, which supplies electric power from the mainbattery 105 to the starter 107 and the electrical loads 113, 114. Inaddition, a current sensor 123 may be inserted in the power supply line,which supplies electric power from the main battery 105 to thesub-battery 106. Also, a voltage sensing means for sensing a voltage ofthe main battery 105 may be provided. Sensed values of the currentsensors 122, 123 and of the voltage sensing means are compared with thevalue of the charge state of the main battery 105. In this way, thepower consumption level and the charge level of the sub-battery 106 maybe sensed with a higher accuracy. Furthermore, the sensed powerconsumption may be corrected by using the more accurate sensed value ofthe charge state of the main battery 105. This allows easy management ofelectrical energy.

Furthermore, even if the detection accuracy of the charge state of thesub-battery 106 itself is poor (the detection precision of leadbatteries is poor), the more accurate detection of the power consumptionof the electrical loads 113, 114 allows more precise detection of thecharge state of the sub-battery 106 by obtaining a difference betweenthe value of the power consumption of the electrical loads 113, 114 andthe discharge amount of the main battery 105.

In the vehicle power supply system according to the thirteenthembodiment, the regenerative energy produced in the alternator 102during vehicle deceleration is recovered directly to thehigh-performance main battery 105 without passing through a DC/DCconverter 111 or the like. In this way, the regenerative energy can berecovered efficiently. Furthermore, electric power is supplied from themain battery 105 to the ordinary electrical loads 113 without passingthrough the DC/DC converter 111 or the like. Thus, the power supply canbe performed efficiently.

Furthermore, one of or both of the main battery 105 and the sub-battery106 is used as the power source of the starter 107 based on the enginetemperature. Thus, the batteries 105, 106 can be effectively usedaccording to the characteristics of the batteries.

Fourteenth Embodiment

Next, a vehicle power supply system according to a fourteenth embodimentwill be described. FIG. 23 is a circuit diagram of the vehicle powersupply system according to the fourteenth embodiment.

In the fourteenth embodiment, power supply to the starter 107 iseffected with one of the main battery 105 and the sub-battery 106. Inthis case, similar to the thirteenth embodiment, the batteries 105, 106are switched by the starter power supply shift switch 116 to supplyelectric power to the starter 107 in the extremely low temperaturerange, the low temperature range and the normal temperature range.However, in this embodiment, the main battery 105 and the sub-battery106 are not used simultaneously to supply electric power to the stator107. Thus, in the high temperature range (T3 or higher) described in thethirteenth embodiment, the sub-battery 106 is used alone to supplyelectric power to the starter 107.

(Variations)

In the thirteenth embodiment according to the second aspect of thepresent invention, there is described the case where the main battery105 and the sub-battery 106 are switched based on the enginetemperature. Alternatively, in place of the above case where the enginetemperature is used to switch between the main battery 105 and thesub-battery 106, the following modification is possible. That is, thebatteries 105, 106 may be switched at the time of initial starting ofthe engine and at the time of restarting the engine after automaticengine stop. More specifically, at the time of initial starting of theengine (i.e., the engine start by turning on of the IG key), it isassumed that the engine temperature is relatively low, so that electricpower is supplied from the sub-battery 106 to the starter 107, andelectric power is supplied from the main battery 105 to the electricalloads 114, which requires the voltage guarantee. In contrast, at thetime of restarting the engine after the automatic engine stop, it isassumed that the engine temperature is relatively high, so that electricpower is supplied from the main battery 105 to the starter 107, andelectric power is supplied from the sub-battery 106 to the electricalloads 114.

Furthermore, in the thirteenth embodiment, there is described theexemplary case where the engine start operation is carried out using thestarter 107 of the belt type, which is given the higher priority thanthe starter 108 of the gear type. Alternatively, the engine startoperation may be carried out using the starter 108 of the gear type byproviding a higher priority to the starter 108 of the gear type than thestarter 107 of the belt type. Further alternatively, the starter 108 ofthe gear type may be used only at the time of initially starting theengine, and the starter 107 of the belt type may be used only at thetime of restarting the engine after the automatic engine stop.

Furthermore, there is described the case where the two starters 107, 108are provided as the starting devices. Alternatively, there may besimilarly used an arrangement where only one of the starter 107 of thebelt type and the starter 108 of the gear type is provided.

In the thirteenth embodiment, there is described the alternator 102,which generates regenerative energy during deceleration of the vehicle.Alternatively, in place of the alternator 102, there may be used a motorgenerator, which has an electric power generating function.

Fifteenth Embodiment

Next, a vehicle power supply system of a fifteenth embodiment accordingto a third aspect of the present application will be described. FIG. 24is an overall construction view of the vehicle power supply systemaccording to the fifteenth embodiment (hereinafter, referred to as asystem S), and FIG. 25 is a control flowchart for the engine startoperation.

The system S includes a generator 201, a first battery 202 and a secondbattery 203 and supply electric power to ordinary electrical loads (alsoreferred to as an ordinary loads 204), important electrical loads (alsoreferred to as an important loads 205) and a starter 206, which are allmounted on the vehicle. The generator 201 is driven by the engine (notshown) to generate electric power. The first battery 202 is charged bythe generator 201. The second battery 203 generates electric power,which has a voltage lower than that of the first battery 202.

The generator 201 is, for example, an alternator, which has an ICregulator and is drive by the engine through a belt. In a good chargestate of the first battery 202, the generator 201 generates electricpower only at the time of decelerating the vehicle (decelerationregeneration) to charge the first battery 202. In other operationalstates of the vehicle (the time of traveling at a steady speed, the timeof acceleration, the time of idling), the power generation by thegenerator 201 is stopped.

The first battery 202 can produce a voltage of, for example, 16 V. Also,the first battery 202 has an internal resistance per unit capacitysmaller than that of the second battery 203, so that the first battery202 is superior in terms of discharge depth and charge acceptancecapability over the second battery 203. The second battery 203 canproduce a voltage of, for example, 12 V and has better low-temperaturedischarge characteristics than the first battery 202.

The first battery 202 and the second battery 203 are connected with eachother through a charging circuit 207 and an assist circuit 208, whichwill be discussed below. The charging circuit 207 is a circuit forsupplying a charging current from the first battery 202 or the generator201 to the second battery 203. This charging circuit 207 is providedwith ON-OFF means (not shown), and the charging current is controlled inaccordance with an ON-OFF cycle of the ON-OFF means.

The assist circuit 208 is a circuit for supplying power from the firstbattery 202 to the starter 206 in addition to the power supply from thesecond battery 203 to the starter 206. The assist circuit 208 isconnected in parallel with the charging circuit 207 between the firstbattery 202 and the second battery 203. The assist circuit 208 isprovided with an ON-OFF switch (not shown). When the ON-OFF switch isturned on, power is supplied from the first battery 202 to the starter206.

The ON-OFF means provided in the charging circuit 207 and the ON-OFFswitch provided in the assist circuit 208 are controlled by anundepicted ECU (Electronic Control Unit).

The ordinary electrical loads (the ordinary electrical loads 204)mounted on the vehicle are connected to the first battery 202 andreceive electric power from the first battery 202. The important loads205, which are involved in a basic running operation or a safetyoperation of the vehicle, are connected to both of the first battery 202and the second battery 203 through a distributor 209, which can controlan output voltage. The important loads 205 can receive electric powerfrom both of the first battery 202 and the second battery 203.

The starter 206 is connected to the second battery 203 and is alsoconnected to the first battery 202 through the charging circuit 207. Thepower supply to the starter 206 will be discussed in detail below.

Next, a control procedure of the system S (at the time of starting theengine) will be described based on a flowchart shown in FIG. 25. First,at step 410, an IG key is turned on (ON). At step 420, electric power issupplied from the second battery 203 to the starter 206.

At step 430, it is determined whether the voltage of the first battery202 is equal to or above a fixed value. When the result of thisdetermination is YES, control proceeds to step 440. In contrast, whenthe determination result is NO, control jumps to step 460 where thepower assistance by the first battery 202 is stopped.

At step 440, a timing for performing the power assistance by the firstbattery 202 is determined. Specifically, it is determined whether thevoltage across the terminals of the second battery 203 has recovered toa predetermined value, or whether fixed time has elapsed from the startof the power supply to the starter 206.

In the same way as discussed above with reference to FIG. 3, the voltageacross the terminals of the second battery 203 drops sharply due to alarge current, which flows through the starter 206 at the time ofinitiating the power supply. Then, the voltage across the terminals ofthe second battery 203 gradually recovers while dipping slightly eachtime a piston passes a top dead center. Accordingly, it is possible todetermine the timing of power assistance from the first battery 202 bymonitoring the voltage across the terminals of the second battery 203.

At step 450, electric power (power assistance) is supplied to thestarter 206 from the first battery 202 through the assist circuit 208.At step 460, it is determined whether the engine has started. Thisdetermination may be made alternatively based on, for example, theengine speed or the voltage across the terminals of the second battery203. When the determination result is YES, control proceeds to step 470.In contrast, when the determination result is NO, control proceeds tostep 480.

At step 470, the IG key is turned from the start position to the OFFposition, and the present operation is terminated. In contrast, at step480, after the shifting of the IG key from the start position to the OFFposition, the present control operation is repeated once again.

According to the power supply system S of the fifteenth embodiment, whenthe power assistance from the first battery 202 is performed at thepredetermined timing after the initiation of the power supply from thesecond battery 203 to the starter 206, the output of the starter 206 isincreased. Thus, the engine can be started more quickly. Particularly,in a vehicle, which has an engine automatic stopping/restarting device(an eco-run system), the engine can be started within a short period oftime at the time of restarting the engine after the automatic stop ofthe engine. Thus, an excellent advantage can be provided.

The first battery 202 has the smaller internal resistance than thesecond battery 203. Thus, as shown in FIG. 26, the voltage drop at thetime of discharging can be limited. As a result, a higher voltage can beapplied to the starter 206. Therefore, the advantage of the power assistby the first battery 202 is further enhanced.

At the initial stage of the engine start operation, electric power issupplied to the starter 206 only from the second battery 203, whichprovides the electric power having the lower voltage. Thus, the load,which is applied to the starter 206, can be reduced in comparison to thecase where the power assistance from the first battery 202, whichprovides the electric power having the higher voltage, is carried outfrom the beginning.

The second battery 203 has better low-temperature dischargecharacteristics over the first battery 202. Thus, the startability ofthe engine at the low temperatures can be improved by using the secondbattery 203 in the first half of the engine start operation where therelatively large current flows in the starter 206. Furthermore, thesecond battery 203 is only used for limited purposes (power supply tothe starter 206 and to the important loads 205). Thus, the lifetime ofthe second battery 203 can be extended, and the reliability of thesystem can be improved.

In the power supply system S of the fifteenth embodiment, the generator201 is connected directly to the first battery 202, which has thesuperior charge acceptance capability due to its internal resistancebeing low. Thus, regenerative energy, which is generated by thegenerator 201 during deceleration of the vehicle, can be efficientlyrecovered to the first battery 202. Furthermore, the generator 201generates electric power and charges the first battery 202 only duringthe deceleration of the vehicle. When the charge state of the firstbattery 202 is good, the generator 201 stops its power generation atother time other than the time of the vehicle deceleration. Thus, theengine load is alleviated, and the fuel consumption is improved.

Also, in the power supply system S of the fifteenth embodiment, electricpower can be supplied to the important loads 205 from both of the firstbattery 202 and the second battery 203 through the distributor 209.Thus, the voltage needed by the important loads 205 can be effectivelysupplied, and the reliability and redundancy of the system are improved.

Furthermore, the assist circuit 208 is provided separately from thecharging circuit 207. Thus, the output characteristics of the starter206 may be switched through use of, for example, simple ON-OFF switch,which is provided on the assist circuit. Therefore, the circuitconstruction and control logic can be simplified to reduce the costs.

In the fifteenth embodiment, there is described the exemplary case wherethe charging current is supplied to the second battery 203 from thefirst battery 202 or the generator 201 through the charging circuit 207.Alternatively, the charging current may be supplied to the secondbattery 203 through the assist circuit 208.

Sixteenth Embodiment

FIG. 27 is an overall construction view of a vehicle power supply system(the system S) according to a sixteenth embodiment, and FIG. 28 is acontrol flowchart for the engine start operation.

The power supply system S has the same basic construction as that of thefifteenth embodiment but shows a more specific example of the firstbattery 202, the second battery 203, the charging circuit 207, theassist circuit 208 and the distributor 209.

The first battery 202 is a Li ion battery, and the second battery 203 isan ordinary Pb battery. Similar to the fifteenth embodiment, the firstbattery 202 has a higher output voltage than the second battery 203 (seeFIG. 27). Also, the first battery 202 has a smaller internal resistanceper unit capacity over the second battery 203.

The charging circuit 207 is provided with a MOSFET 207 a, which servesas an ON-OFF means. Turning on and off of the MOSFET 207 a is controlledat a certain time rate by a power source monitor ECU 210. A relay 208 a,which serves as an ON-OFF switch, is arranged in the assist circuit 208.At the time of performing the power assistance from the first battery202, the relay 208 a is turned on by the power source monitor ECU 210.

The distributor 209 includes a DC/DC converter 209 a and a diode 209 b.The DC/DC converter 209 a is provided between the first battery 202 andthe important loads 205. The diode 209 b is provided between the secondbattery 203 and the important loads 205. The DC/DC converter 209 a iscontrolled by the power source monitor ECU 210. Particularly, at thetime of stopping the engine, operation of the DC/DC converter 209 a isstopped by the power source monitor ECU 210 to limit flow of a darkcurrent from the first battery 202 to the important loads 205. Thus, atthe time of stopping the engine, the dark current is provided to theimportant loads from the second battery 203.

The power source monitor ECU 210 monitors the voltage across theterminals of the first battery 202 and the voltage across the terminalsof the second battery 203. Based on the charge state of the firstbattery 202 and the charge state of the second battery 203, the powersource monitor ECU 210 controls the MOSFET 207 a, the relay 208 a andthe DC/DC converter 209 a.

A control procedure (shown in the flowchart of FIG. 28) at the time ofstarting the engine through use of the power source monitor ECU 210 isthe same as that of the fifteenth embodiment, and thus will not bedescribed here for the sake of simplicity.

In the present embodiment, the MOSFET 207 a is provided in the chargingcircuit 207. Thus, through the ON-OFF control operation of the MOSFET207 a, the charging current, which is supplied from the first battery202 to the second battery 203, can be easily controlled.

Furthermore, the assist circuit 208 is provided only with the simplerelay 208 a. The power assistance from the first battery 202 to thestarter 206 can be controlled based on the ON-OFF state of the relay 208a. Thus, the output characteristics of the starter 206 can be easilyswitched.

The distributor 209 includes the combination of the DC/DC converter 209a and the diode 209 b. Thus, at the time of engine stop, the DC/DCconverter 209 a may be turned off to limit supply of the dark currentfrom the first battery 202 to the important load 205 at the time ofengine stop. Therefore, the load on the first battery 202 can bealleviated. As a result, downsizing (cost reduction) of the firstbattery 202, which uses the expensive Li ion battery, can be achieved.

Seventeenth Embodiment

FIG. 29 is an overall construction view of a vehicle power supply system(the system S) according to a seventeenth embodiment. The seventeenthembodiment is an exemplary case, which indicates power supply toordinary loads 204 a, which require a dark current, and power supply toordinary loads 204 b, which do not require a dark current, among theordinary electrical loads.

Similar to the fifteenth and sixteenth embodiments, the ordinary loads204 b, which do not require the dark current, are connected to the firstbattery 202 and receive electric power from the first battery 202. Incontrast, the ordinary loads 204 a, which require the dark current, isconnected to the second battery 203 and receive the dark current fromthe second battery 203.

As discussed above, the ordinary loads 204 are divided to the highvoltage side and the low voltage side based on the need of the darkcurrent. Thus, when the engine is stopped, the first battery 202 willnot be used. As a result, the first battery 202 with a smaller capacitycan be reduced to limit or reduce the costs of the first battery 202.

Eighteenth Embodiment

FIG. 30 is an overall construction view of a vehicle power supply system(the system S) according to an eighteenth embodiment. The system S has agenerator 201, which has a power converter (e.g., a DC/DC converter).The output voltage of the generator 201 is variable by the powerconverter of the generator 201.

With this construction, a charging current can be supplied to the secondbattery 203 from the first battery 202 or from the generator 201 throughthe power converter. Thus, the charging circuit 207, which is recited inthe fifteenth to seventeenth embodiments, can be eliminated. As aresult, the circuit construction of the overall system can besimplified.

(Variations)

In the sixteenth embodiment, the MOSFET 207 a is used as the ON-OFFmeans provided in the charging circuit 207. Alternatively, it is alsopossible to use a relay in place of the MOSFET 207 a. Similarly, in thesixteenth embodiment, the relay 208 a is used as the ON-OFF switchprovided in the assist circuit 208. Alternatively, a semiconductorswitch may be used in place of the relay 208 a.

The first battery 202 and the second battery 203 are described as the Liion battery and the Pb battery, respectively. However, the invention isnot limited to this construction.

Furthermore, in the fifteenth embodiment, the alternator is used as thegenerator 201. Alternatively, a motor generator, which has a powergenerating function, may be used in place of the alternator.

1. A vehicle power supply system comprising: a generator, which ismounted on a vehicle; a main power source, to which an ordinary load isconnected; an auxiliary power source, which is connected to thegenerator, wherein the auxiliary power source recovers regenerativeelectric power, which is generated by the generator using kinetic energyor thermal energy, and the auxiliary power source stores electric powerthat is generated by the generator; a first supply circuit, whichconnects the auxiliary power source to the main power source and theordinary load through a DC/DC converter; a second supply circuit, whichis in parallel with the first supply circuit and which connects theauxiliary power source to the main power source and the ordinary loadthrough a switch; and a control means for controlling operation of theDC/DC converter and operation of the switch, wherein the control meansis enabled to select one of: a first control state, in which the DC/DCconverter is driven, and the switch is opened; and a second controlstate, in which the DC/DC converter is stopped, and the switch isclosed.
 2. A vehicle power supply system comprising: a generator, whichis driven by an engine to generate electric power; a main power source,to which an ordinary load, such as a lamp or an audio device, isconnected; an auxiliary power source, which is connected to thegenerator, wherein the auxiliary power source recovers regenerativeelectric power, which is generated by the generator at time ofdeceleration of a vehicle, and the auxiliary power source storeselectric power that is generated by the generator through driving of thegenerator by the engine; a first supply circuit, which connects theauxiliary power source to the main power source and the ordinary loadthrough a DC/DC converter; a second supply circuit, which is in parallelwith the first supply circuit and which connects the auxiliary powersource to the main power source and the ordinary load through a switch;and a control means for controlling operation of the DC/DC converter andoperation of the switch, wherein the control means is enabled to selectone of: a first control state, in which the DC/DC converter is driven,and the switch is opened; and a second control state, in which the DC/DCconverter is stopped, and the switch is closed.
 3. The vehicle powersupply system according to claim 1, wherein the control means is alsoenabled to select a third control state, in which the DC/DC converter isdriven, and the switch is closed.
 4. The vehicle power supply systemaccording to claim 1, wherein the main power source has a greaternominal voltage or nominal capacity over the auxiliary power source. 5.The vehicle power supply system according to claim 1, wherein the mainpower source has a smaller nominal voltage or nominal capacity over theauxiliary power source.
 6. The vehicle power supply system according toclaim 1, wherein the main power source and the auxiliary power sourcehave a common operational range, in which a working voltage of the mainpower source generally coincides with a working voltage of the auxiliarypower source.
 7. The vehicle power supply system according to claim 1,wherein the main power source has greater low-temperature dischargecharacteristics than the auxiliary power source.
 8. The vehicle powersupply system according to claim 1, wherein the auxiliary power sourcehas a greater charge acceptance capability and a greater statedetectability than the main power source.
 9. The vehicle power supplysystem according to claim 1, wherein: the main power source is one of alead battery, a Li ion battery and a Ni hydrogen battery; and theauxiliary power source is one of a lead battery, a Li ion battery, a Nihydrogen battery and an electrical double-layer capacitor.
 10. Thevehicle power supply system according to claim 1, wherein at time ofsupplying power from the auxiliary power source to the main power sourceand the ordinary load, the control means selects the second controlstate when the voltage of the auxiliary power source has fallen to orbelow an allowable rated voltage of the ordinary load.
 11. The vehiclepower supply system according to claim 1, wherein the control meansselects one of the first control state and the second control state inaccordance with the power supply level, and the power supply level is alevel of power supplied from the auxiliary power source to the mainpower source and the ordinary load, or a level of power supplied fromthe main power source to the auxiliary power source and the ordinaryload.
 12. The vehicle power supply system according to claim 11,wherein: the control means selects the first control state when thepower supply level is equal to or below a predetermined value; and thecontrol means selects the second control state when the power supplylevel is above the predetermined value.
 13. The vehicle power supplysystem according to claim 1, wherein the control means selects one ofthe first control state and the second control state in accordance witha voltage difference between the main power source and the auxiliarypower source.
 14. The vehicle power supply system according to claim 13,wherein: the control means selects the second control state when thevoltage difference between the main power source and the auxiliary powersource is equal to or below a predetermined value; and the control meansselects the first control state when the voltage difference between themain power source and the auxiliary power source is above thepredetermined value.
 15. The vehicle power supply system according toclaim 1, wherein the control means selects one of the first controlstate and the second control state in accordance with: a voltagedifference between the main power source and the auxiliary power source;and a level of power supplied from the auxiliary power source to themain power source and the ordinary load, or a level of power suppliedfrom the main power source to the auxiliary power source and theordinary load.
 16. The vehicle power supply system according to claim15, wherein: the control means first selects the first control statewhen the voltage of the auxiliary power source is higher than that ofthe main power source and also the power level supplied from theauxiliary power source to the main power source and the ordinary load isgreater than a predetermined value; and the control means then shiftsfrom the first control state to the second control state after thevoltage of the auxiliary power source falls to or below the allowablerated voltage of the ordinary load.
 17. The vehicle power supply systemaccording to claim 1, further comprising: a third supply circuit, whichsupplies electric power from the auxiliary power source to an importantload, which is involved in a basic running operation or a safetyoperation of the vehicle; and a fourth supply circuit, which supplieselectric power from the main power source to the important load, whereineach of the third supply circuit and the fourth supply circuit has adiode, which limits a reverse flow of an electric current therethrough.18. The vehicle power supply system according to claim 1, furthercomprising: a third supply circuit, which supplies electric power fromthe auxiliary power source to an important load, which is involved in abasic running operation or a safety operation of the vehicle; and afourth supply circuit, which supplies electric power from the main powersource to the important load, wherein the third supply circuit has adiode, which limits a reverse flow of an electric current therethrough,in a case where the main power source has a higher nominal voltage ornominal capacity over the auxiliary power source.
 19. The vehicle powersupply system according to claim 1, further comprising: a third supplycircuit, which supplies electric power from the auxiliary power sourceto an important load, which is involved in a basic running operation ora safety operation of the vehicle; and a fourth supply circuit, whichsupplies electric power from the main power source to the importantload, wherein the fourth supply circuit has a diode, which limits areverse flow of an electric current therethrough, in a case the mainpower source has a lower nominal voltage or nominal capacity over theauxiliary power source.
 20. The vehicle power supply system according toclaim 17, wherein the control means opens the switch when one of themain power source and the auxiliary power source fails in a state wherethe second control state is selected by the control means.
 21. Thevehicle power supply system according to claim 20, wherein the controlmeans opens the switch when short-circuiting occurs between a cathodeand an anode of one of the main power source and the auxiliary powersource.
 22. The vehicle power supply system according to claim 17,wherein the control means opens the switch when performance of the mainpower source falls.
 23. The vehicle power supply system according toclaim 17, wherein the control means opens the switch when performance ofthe auxiliary power source falls.
 24. The vehicle power supply systemaccording to claim 20, wherein the control means stops the DC/DCconverter when one of the main power source and the auxiliary powersource fails in a state where the first control state is selected by thecontrol means.
 25. The vehicle power supply system according to claim 3,wherein the control means switches from the second control state to thethird control state when a temperature of the switch is increased beyonda predetermined value in a state where the second control state isselected by the control means.
 26. The vehicle power supply systemaccording to claim 1, wherein the ordinary load, which is connected tothe main power source, includes an electrical load, which requires adark current after stopping of the engine.
 27. The vehicle power supplysystem according to claim 1, wherein at time of shifting from the firstcontrol state to the second control state or at time of shifting fromthe second control state to the first control state, the control meansincreases an output voltage of the DC/DC converter to a higher one of avoltage of the main power source and a voltage of the auxiliary powersource or decreases the output voltage of the DC/DC converter to a lowerone of the voltage of the main power source and the voltage of theauxiliary power source, and then the control means shifts from the firstcontrol state to the second control state or shifts from the secondcontrol state to the first control state.
 28. The vehicle power supplysystem according to claim 1, wherein: the control means senses a workingparameter, such as a temperature or a voltage, of the DC/DC converter ina state where the first control state is selected by the control means;and the control means shifts from the first control state to the secondcontrol state when the sensed working parameter of the DC/DC converterexceeds a predefined value.
 29. The vehicle power supply systemaccording to claim 1, wherein the control means controls an outputvoltage of the DC/DC converter such that the output voltage of the DC/DCconverter substantially coincides with an output voltage of thegenerator when the first control state is selected by the control means.30. The vehicle power supply system according to claim 1, wherein thecontrol means controls an output voltage of the generator such that theoutput voltage of the generator substantially coincides with an outputvoltage of the DC/DC converter when the first control state is selectedby the control means.
 31. The vehicle power supply system according toclaim 1, wherein the control means senses a charge acceptance capabilityof the main power source based on an output state of the DC/DC converterwhen the first control state is selected by the control means.
 32. Thevehicle power supply system according to claim 1, wherein: the controlmeans senses a voltage of the auxiliary power source and an outputvoltage of the DC/DC converter based on a running state of the vehicle;and the control means controls an output of the generator based on asensed result of the voltage of the auxiliary power source and of theoutput voltage of the DC/DC converter.
 33. The vehicle power supplysystem according to claim 1, wherein the auxiliary power source supplieselectric power to an electrical load, which does not require a darkcurrent.
 34. The vehicle power supply system according to claim 33,wherein the electrical load, which does not require the dark current, isone of: a first electrical load that does not have an internal memory;and a second electrical load that always uses an initial constant of aninternal memory.
 35. The vehicle power supply system according to claim1, further comprising a dark current blocking means for blocking thedark current, wherein the auxiliary power source supplies electric powerto an electrical load, which does not require the dark current.
 36. Thevehicle power supply system according to claim 1, wherein an auxiliarypower source switch is connected in series with the auxiliary powersource.
 37. The vehicle power supply system according to claim 36,wherein the auxiliary power source switch is disposed between thegenerator and the auxiliary power source in such a manner that theauxiliary power source switch is positioned on a generator side of aninput side connection of the DC/DC converter.
 38. The vehicle powersupply system according to claim 1, wherein the DC/DC converter includesa series regulator.
 39. The vehicle power supply system according toclaim 1, wherein in a case where a fully charged state of the auxiliarypower source is sensed at time of performing regenerative powergeneration of the generator, the generator carries out the regenerativepower generation at a voltage that is lower than a voltage of theauxiliary power source measured in the fully charged state of theauxiliary power source and supplies electric power to the ordinary loadin one of the first control state and the second control state.
 40. Thevehicle power supply system according to claim 3, wherein in a casewhere a fully charged state of the auxiliary power source is sensed attime of performing regenerative power generation of the generator, thegenerator carries out the regenerative power generation at a voltagethat is lower than a voltage of the auxiliary power source measured inthe fully charged state of the auxiliary power source and supplieselectric power to the ordinary load in one of the first control state,the second control state and the third control state.
 41. The vehiclepower supply system according to claim 1, wherein the main power sourceis maintained in a fully charged state in the first control state.
 42. Avehicle power supply system comprising: a generating means forgenerating regenerative energy at time of decelerating a vehicle; ahigh-performance main power storage means for directly storing theregenerative energy, which is generated by the generating means, and forsupplying electric power to an electrical load, which is mounted on thevehicle; an auxiliary power storage means for receiving and storing theelectric power supplied from the main power storage means, wherein theauxiliary power storage means has a greater discharge characteristics ata low temperature than the main power storage means; and a startingdevice power source switching means for selecting one or both of themain power storage means and the auxiliary power storage means as apower source based on an engine starting temperature to supply electricpower to a starting device for starting an engine at time of startingthe engine, wherein the engine starting temperature is an enginetemperature or an engine related temperature, which is measured at thetime of starting the engine.
 43. The vehicle power supply systemaccording to claim 42, wherein: a temperature range below apredetermined temperature T1 is an extremely low temperature range; atemperature range between the predetermined temperature T1 and apredetermined temperature T2 (T1<T2) is a low temperature range; atemperature range between the predetermined temperature T2 and apredetermined temperature T3 (T2<T3) is a normal temperature range; atemperature range above the predetermined temperature T3 is a hightemperature range; the starting device power source switching meansselects the main power storage means when the engine startingtemperature is in the normal temperature range; and the starting devicepower source switching means switches to use both the main power storagemeans and the auxiliary power storage means when the engine startingtemperature is in one of the extremely low temperature range and thehigh temperature range.
 44. The vehicle power supply system according toclaim 42, wherein the auxiliary power storage means supplies electricpower to the starting device at the time of starting the engine when theengine starting temperature is in the low temperature range.
 45. Thevehicle power supply system according to claim 43, wherein: theauxiliary power storage means supplies electric power to the electricalload, which requires a guaranteed voltage, when the main power storagemeans supplies electric power to the starting device at the time ofstarting the engine; and the main power storage means supplies electricpower to the electrical load, which requires the guaranteed voltage,when the auxiliary power storage means supplies electric power to thestarting device at the time of starting the engine.
 46. A vehicle powersupply system comprising: a generating means for generating regenerativeenergy at time of decelerating a vehicle; a high-performance main powerstorage means for directly storing the regenerative energy, which isgenerated by the generating means, and for supplying electric power toan electrical load, which is mounted on the vehicle; an auxiliary powerstorage means for receiving and storing the electric power supplied fromthe main power storage means, so that the auxiliary power storage meansis charged, wherein the auxiliary power storage means has superiordischarge characteristics at a low temperature over the main powerstorage means; an automatic engine stopping/starting control device,which automatically controls stopping and restarting of an engine; and astarting device power source switching means for selecting one of theauxiliary power storage means and the main power storage means as apower source to supply electric power to a starting device for startingthe engine, wherein the starting device power source switching meansselects the auxiliary power storage means at time of starting the enginefirst time and selects the main power storage means at time ofrestarting the engine through use of the automatic enginestopping/starting control device.
 47. The vehicle power supply systemaccording to claim 46, wherein: the main power storage means provideselectric power to the electrical load, which requires a guaranteedvoltage, at the time of starting the engine first time; and theauxiliary power storage means provides electric power to the electricalload, which requires the guaranteed voltage, at the time of restartingthe engine through use of the automatic engine stopping/starting controldevice.
 48. The vehicle power supply system according to claim 46,wherein the main power storage means provides electric power to theelectrical load while the engine is automatically stopped.
 49. Thevehicle power supply system according to claim 48, further comprising astate sensing means for sensing a charge state of the main power storagemeans, wherein when it is determined that the main power storage meansalone is not enough to supply start-up electric power to the startingdevice based on a sensed result of the state sensing means, the start-upelectric power is supplied to the starting device from the auxiliarypower storage means alone or from both the auxiliary power storage meansand the main power storage means.
 50. The vehicle power supply systemaccording to claim 42, further comprising a charging circuit, whichsupplies electric power from the main power storage means to theauxiliary power storage means, wherein: the charging circuit includes aDC/DC converter; and the auxiliary power storage means is charged with amicro current, which is supplied from the main power storage means tothe auxiliary power storage means through the DC/DC converter.
 51. Thevehicle power supply system according to claim 42, further comprising acharging circuit, which supplies electric power from the main powerstorage means to the auxiliary power storage means, wherein: thecharging circuit includes a relay switch; and the auxiliary powerstorage means is charged with electric power supplied from the mainpower storage means when the relay switch is turned on.
 52. The vehiclepower supply system according to claim 50, wherein when a voltagedifference between the main power storage means and the auxiliary powerstorage means is smaller than a predetermined value, the DC/DC converteris operated, so that the auxiliary power storage means is charged withelectric power supplied from the main power storage means.
 53. Thevehicle power supply system according to claim 50, wherein the auxiliarypower storage means is charged with electric power supplied from themain power storage means when the generating means stops its powergenerating operation.
 54. The vehicle power supply system according toclaim 42, further comprising: a current sensing means that is providedin a conductor portion, which supplies electric power from the mainpower storage means to the starting device and the electrical load; acurrent sensing means that is provided in a conductor portion, whichsupplies electric power from the main power storage means to theauxiliary power storage means; and a voltage sensing means for sensing avoltage of the main power storage means, wherein a measured value ofeach current sensing means and a measured value of the voltage sensingmeans are compared with a measured value of the charge state of the mainpower storage means obtained through the state sensing means, so that apower consumption level and a charge level of the auxiliary powerstorage means are sensed with relatively high accuracy.
 55. The vehiclepower supply system according to claim 42, wherein when the charge levelof the main power storage means deviates from a predetermined level themain power storage means is switched to the auxiliary power storagemeans to supply electric power to the electrical load, which requires aguaranteed voltage.
 56. The vehicle power supply system according toclaim 42, wherein supply of a dark current is performed from the mainpower storage means after the engine is stopped through operation of akey by a driver.
 57. A vehicle power supply system comprising: agenerator, which is driven by an engine to generate electric power; afirst battery, which is charged with electric power generated by thegenerator; a second battery, which has an output voltage lower than thatof the first battery, wherein the second battery supplies electric powerto a starter at time of starting the engine; a charging circuit, whichsupplies electric power from one of the generator and the first batteryto the second battery; and an assist circuit, which provides powerassistance from the first battery to the starter in addition to powersupply from the second battery to the starter.
 58. The vehicle powersupply system according to claim 57, wherein the power assistance fromthe first battery is executed at a predetermined time after initiationof the power supply from the second battery to the starter.
 59. Thevehicle power supply system according to claim 58, wherein thepredetermined time at which the power assistance from the first batteryis executed, is determined based on elapsed time since the time ofstarting the engine or based on transition of a voltage value of thesecond battery.
 60. The vehicle power supply system according to claim57, wherein an internal resistance per unit capacity of the firstbattery is smaller than that of the second battery.
 61. The vehiclepower supply system according to claim 58, wherein the power assistancefrom the first battery is stopped when the voltage of the first batteryis lower than a predetermined value.
 62. The vehicle power supply systemaccording to claim 57, wherein the second battery has greaterlow-temperature discharge characteristics than the first battery. 63.The vehicle power supply system according to claim 57, wherein: thecharging circuit includes an ON-OFF means for turning on and turning offsupply of the electric power to the second battery at a certain timeratio between an ON time period and an OFF time period; and the assistcircuit includes one of a relay and a semiconductor switch.
 64. Thevehicle power supply system according to claim 63, wherein the ON-OFFmeans, which is provided in the charging circuit, is an electronicswitching device that uses a semiconductor.
 65. The vehicle power supplysystem according to claim 63, wherein the ON-OFF means, which isprovided in the charging circuit, is a DC/DC converter.
 66. The vehiclepower supply system according to claim 65, wherein the DC/DC converteris provided in the generator.
 67. The vehicle power supply systemaccording to claim 57, further comprising a distributor, which isconnected to the first battery and the second battery to control anoutput voltage of the first battery and an output voltage of the secondbattery, wherein supply of electric power to an important load, which isinvolved in a basic running operation or a safety operation of avehicle, is carried out through the distributor.
 68. The vehicle powersupply system according to claim 57, wherein the first battery storesregenerative energy, which is generated by the generator at time ofdecelerating a vehicle.
 69. The vehicle power supply system according toclaim 57, wherein the second battery provides dark current to anelectrical load after the engine is stopped through operation of a keyby a driver.
 70. The vehicle power supply system according to claim 57,wherein the vehicle power supply system is applied to a vehicle that hasan automatic engine stopping/starting control device, whichautomatically controls stopping and restarting of the engine.
 71. Thevehicle power supply system according to claim 51, wherein when avoltage difference between the main power storage means and theauxiliary power storage means is smaller than a predetermined value, therelay switch is turned on, so that the auxiliary power storage means ischarged with electric power supplied from the main power storage means.72. The vehicle power supply system according to claim 1, wherein theordinary load includes a lamp or an audio device; the kinetic energyincludes kinetic energy of deceleration; and the thermal energy includesthermal energy of exhaust heat.